Saturday, January 25, 2020
Causes, Symptoms and Treatments of Anaemia
Causes, Symptoms and Treatments of Anaemia 1. Introduction Anaemia is a syndrome characterised by a lack of healthy red blood cells or haemoglobin deficiency in the red blood cells, resulting in inadequate oxygen supply to the tissues. The condition can be temporary, long-term or chronic, and of mild to severe intensity. There are many forms and causes of anaemia. Normal blood consists of three types of blood cells: white blood cells (leucocytes), platelets and red blood cells (erythrocytes). The first generation of erythrocyte precursors in the developing foetus are produced in the yolk sac. They are carried to the developing liver by the blood where they form mature red blood cells that are required to meet the metabolic needs of the foetus. Until the 18th week of gestation, erythrocytes are produced only by liver after which the production shifts to the spleen and the bone marrow. The life of a red blood cell is about 127 days or 4 months (Shemin and Rittenberg, 1946; Kohgo et al., 2008). The main causes of anaemia are blood loss, product ion of too few red blood cells by the bone marrow or a rapid destruction of cells.           Haemoglobin, a protein, present in the red blood cells is involved in the transport of oxygen from the lungs to all the other organs and tissues of the body. Iron is an important constituent of the haemoglobin protein structure which is intimately involved in the transport of oxygen. Anaemia is generally defined as a lower than normal haemoglobin concentration. The normal blood haemoglobin concentration is dependent on age and sex, and, according to the World Health Organisation (WHO) Expert Committee Report, anaemia results when the blood concentration of haemoglobin falls below 130 g/L in men or 120 g/L in non-pregnant women (WHO, 1968). However, the reference range of haemoglobin concentration in blood could vary depending on the ethnicity, age, sex, environmental conditions and food habits of the population analysed. According to Beutler and Warren (2006), more reasonable benchmarks for anaemia are 137 g/L for white men aged between 20 and 60 years and 132 g/L for older men. The value for women of all ages would be 122 g/L. Also, the lower limit of normal of haemoglobin concentrations of African Americans are appreciably lower than that of Caucasians (Beutler and Warren, 2006).           Besides the well recognised iron deficiency anaemia, several inherited anaemias are also known. These are mostly haemoglobinopathies. Adult haemoglobin is a tetrameric haeme-protein. Abnormalities of beta-chain or alpha-chain produce the various medically significant haemoglobinopathies. The variations in amino acid composition induced genetically impart marked differences in the oxygen carrying properties of haemoglobin. Mutations in the haemoglobin genes cause disorders that are qualitative abnormalities in the synthesis of haemoglobin (e.g., sickle cell disease) and some that are quantitative abnormalities that pertain to the rate of haemoglobin synthesis (e.g., the thalassemias) (Weatherall., 1969). In SCD, the missense mutation in the ÃŽ ²-globin gene causes the disorder. The mutation causing sickle cell anemia is a single nucleotide substitution (A to T) in the codon for amino acid 6. The substitution converts a glutamic acid codon (GAG) to a valine codon (GTG). The form of haemoglobin in persons with sickle cell anemia is referred to as HbS. Also, the valine for glutamic acid replacement causes the haemoglobin tetramers to aggregate into arrays upon deoxygenation in the tissues. This aggregation leads to deformation of the red blood cell making it relatively inflexible and restrict its movement in the capillary beds. Repeated cycles of oxygenation and deoxygenation lead to irreversible sickling and clogging of the fine capillaries. Incessant clogging of the capillary beds damages the kidneys, heart and lungs while the constant destruction of the sickled red blood cells triggers chronic anaemia and episodes of hyperbilirubinaemia.           Fanconi anaemia (FA) is an autosomal recessive condition, and the most common type of inherited bone marrow failure syndrome. The clinical features of FA are haematological with aplastic anaemia, myelodysplastic syndrome (MDS), and acute myeloid leukaemia (AML) being increasingly present in homozygotes (Tischkowitz and Hodgson, 2003). Cooleys anaemia is yet another disorder caused by a defect in haemoglobin synthesis.           Autoimmune haemolytic anaemia is a syndrome in which individuals produce antibodies directed against one of their own erythrocyte membrane antigens. The condition results in diminished haemoglobin concentrations on account of shortened red blood cell lifespan (Sokol et al., 1992).           Megaloblastic anaemia is a blood disorder in which anaemia occurs with erythrocytes which are larger in size than normal. The disorder is usually associated with a deficiency of vitamin B12 or folic acid . It can also be caused by alcohol abuse, drugs that impact DNA such as anti-cancer drugs, leukaemia, and certain inherited disorders among others (Dugdale, 2008).           Malaria causes increased deformability of vivax-infected red blood cells (Anstey et al., 2009). Malarial anaemia occurs due to lysis of parasite-infected and non-parasitised erythroblasts as also by the effect of parasite products on erythropoiesis (Ru et al., 2009).           Large amounts of iron are needed for haemoglobin synthesis by erythroblasts in the bone marrow. Transferrin receptor 1 (TfR1) expressed highly in erythroblasts plays an important role in extracellular iron uptake (Kohgo et al., 2008). Inside the erythroblasts, iron transported into the mitochondria gets incorporated into the haeme ring in a multistep pathway. Genetic abnormalities in this pathway cause the phenotype of ringed sideroblastic anemias (Fleming, 2002). The sideroblastic anemias are a heterogeneous group of acquired and inherited bone marrow disorders, characterised by mitochondrial iron overload in developing red blood cells. These conditions are diagnosed by the presence of pathologic iron deposits in erythroblast mitochondria (Bottomley, 2006).  2. Classification of anaemia Anaemia can be generally classified based on the morphology of the red blood cells, the pathogenic spectra or clinical presentation (Chulilla et al., 2009). The morphological classification is based on mean corpuscular volume (MCV) and comprises of microcytic, macrocytic and normocytic anaemia.      (a) Microcytic anaemia refers to the presence of RBCs smaller than normal volume, the reduced MCV ( 15 would probably indicate IDA (Chulilla et al., 2009).           In macrocytic anaemia, erythrocytes are larger (MCV > 98 fL) than their normal volume (MCV = 82-98 fL). Vitamin B12 deficiency leads to delayed DNA synthesis in rapidly growing hematopoietic cells, and can result in macrocytic anemia. Drugs that interfere with nucleic acid metabolism, such as.hydroxyurea increases MCV (> 110 fL) while alcohol induces a moderate macrocytosis (100-110 fL). In the initial stage, most anaemias are normocytic. The causes of normocytic anaemia are nutritional deficiency, renal failure and haemolytic anemia (Tefferi, 2003). The most common normocytic anaemia in adults is anaemia of chronic disease (ACD) (Krantz, 1994). Common childhood normocytic anaemias are, besides iron deficiency anaemia, those due to acute bleeding, sickle cell anemia, red blood cell membrane disorders and current or recent infections especially in the very young (Bessman et al., 1983). Homozygous sickle cell disease is the most common cause of h aemolytic normocytic anemias in children (Weatherall DJ, 1997a).           In practice, the morphological classification is quicker and therefore, more useful as a diagnostic tool. Besides, MCV is also closely linked to mean corpuscular haemoglobin (MCH), which denotes mean haemoglobin per erythrocyte expressed in picograms (Chulilla et al., 2009). Thus, MCV and MCH decrease simultaneously in microcytic, hypochromic anemia and increase together in macrocytic, hyperchromic anemia.           Pathogenic classification of anaemia is based on the production pattern of RBC: whether anaemia is due to inadequate production or loss of erythrocytes caused by bleeding or haemolysis. This approach is useful in those cases where MCV is normal. Pathogenic classification is also essential for proper recognition of the mechanisms involved in the genesis of anaemia. Based on the pathogenic mechanisms, anaemia is further divided into two types namely, (i) hypo-regenerative in which the bone marrow production of erythrocytes is decreased because of impaired function, decreased number of precursor cells, reduced bone marrow infiltration, or lack of nutrients; and (ii) regenerative: when bone marrow upregulates the production of erythrocytes in response to the low erythrocyte mass (Chulilla et al., 2009). This is typified by increased generation of erythropoietin in response to lowered haemoglobin concentration, and also reflects a loss of erythrocyt es, due to bleeding or haemolysis. The reticulocyte count is typically higher.           Sickle cell disease is characterised by sickled red cells. The first report of SCD was published a century ago noting the presence of peculiar elongated cells in blood by James Herrick, an American physician (1910). Pauling et al. (1949) described it as a molecular disease. The molecular nature of sickle haemoglobin (Hb S) in which valine is substituted for glutamic acid at the sixth amino acid position in the beta globin gene reduces the solubility of Hb, causing red cells to sickle (Fig. 1). Sickling of cells occurs at first reversibly, then finally as a state of permanent distortion, when cells containing HbS and inadequate amounts of other haemoglobins including foetal haemoglobin, which retards sickling, become deoxygenated (Bunn, 1997). The abnormal red cells break down, leading to anaemia, and clog blood vessels with aggregates, leading to recurrent episodes of severe pain and multiorgan ischaemic damage (Creary et al., 2007). The high levels of inflammatory cytokines in SCD may promote retention of iron by macrophage/reticuloendothelial cells and/or renal cells. SCD care commonly depends on transfusion that results in iron overload (Walter et al., 2009). 3. Pathogenesis of anaemia Anaemia is a symptom , or a syndrome, and not a disease (Chulilla et al., 2009). Several types of anaemia have been recognised, the pathogenesis of each being unique. Iron deficiency anaemia (IDA) is the most common type of anaemia due to nutritional causes encountered worldwide (Killip et al., 2008). Iron is one of the essential micronutrients required for normal erythropoietic function While the causes of iron deficiency vary significantly depending on chronological age and gender, IDA can reduce work capacity in adults (Haas Brownlie, 2001) and affect motor and mental development in children (Halterman et al., 2001). The metabolism of iron is uniquely controlled by absorption rather than excretion (Siah et al., 2006). Iron absorption typically occurring in the duodenum accounts for only 5 to 10 per cent of the amount ingested in homoeostatis. The value decreases further under conditions of iron overload, and increases up to fivefold under conditions of iron depletion (Killip et al., 2008). Iron is ingested as haem iron (10%) present in meat, and as non-haem ionic form iron (90%) found in plant and dairy products. In the absence of a regulated excretion of iron through the liver or kidneys, the only way iron is lost from the body is through bleeding and sloughing of cells. Thus, men and non-menstruating women lose about 1 mg of iron per day while menstruating women could normally lose up to 1.025 mg of iron per day (Killip et al., 2008). The requirements for erythropoiesis which are typically 20-30 mg/day are dependent on the internal turnover of iron (Munoz et al., 2009) For example, the amount of iron required for daily production of 300 billion RBCs (20-30 mg) is provided mostly by recycling iron by macrophages (Andrews, 1999).           Iron deficiency occurs when the metabolic demand for iron exceeds the amount available for absorption through consumption. Deficiency of nutritional intake of iron is important, while abnormal iron absorption due to hereditary or acquired iron-refractory iron deficiency anemia (IRIDA) is another important cause of unexplained iron deficiency. However, IDA is commonly attributed to blood loss e.g., physiological losses in women of reproductive age. It might also represent occult bleeding from the gastrointestinal (GI) tract generally indicative of malignancy (Hershko and Skikne, 2009).           Iron absorption and loss play an important role in the pathogenesis and management of IDA. Human iron disorders are necessarily disorders of iron balance or iron distribution. Iron homeostasis involves accurate control of intestinal iron absorption, efficient utilisation of iron for erythropoiesis, proper recycling of iron from senescent erythrocytes, and regulated storage of iron by hepatocytes and macrophages (Andrews, 2008). Iron deficiency is largely acquired, resulting from blood loss (e.g., from intestinal parasitosis), from inadequate dietary iron intake, or both. Infections, for example, with H pylori, can lead to profound iron deficiency anemia without significant bleeding. Genetic defects can cause iron deficiency anaemia. Mutations in the genes encoding DMT1 (SLC11A2) and glutaredoxin 5 (GLRX5) lead to autosomal recessive hypochromic, microcytic anaemia (Mims et al., 2005). Transferrin is a protein that keeps iron nonreactive in the circulation, and delivers iron to cells possessing specific transferrin receptors such as TFR1 which is found in largest amounts on erythroid precursors. Mutations in the TF gene leading to deficiency of serum transferrin causes disruption in the transfer of iron to erythroid precursors thereby producing an enormous increase in intestinal iron absorption and consequent tissue iron deposition (Beutler et al., 2000). Quigley et al. (2004) found a haem exporter, FLVCR, which appears to be necessary for normal erythroid development. Inactivation of FLVCR gene after birth in mice led to severe macrocytic anaemia, indicating haem export to be important for normal erythropoiesis.           The anaemia of chronic disease (ACD) found in patients with chronic infectious, inflammatory, and neoplastic disorders is the second most frequently encountered anaemia after iron-deficiency anaemia. It is most often a normochromic, normocytic anaemia that is primarily caused by an inadequate production of red cells, with low reticulocyte production (Krantz, 1994). The pathogenesis of ACD is unequivocally linked to increased production of the cytokines including tumour necrosis factor, interleukin-1, and the interferons that mediate the immune or inflammatory response. The various processes leading to the development of ACD such as reduced life span of red cells, diminished erythropoietin effect on anaemia, insufficient erythroid colony formation in response to erythropoietin, and impaired bioavailability of reticuloendothelial iron stores appear to be caused by inflammatory cytokines (Means, 1996;2003). Although iron metabolism is characterist ically impaired in ACD, it may not play a key role in the pathogenesis of ACD (Spivak, 2002). Neither is the lack of available iron central to the pathogenesis of the syndrome, according to Spivak (2002), who found reduced iron absorption and decreased erythroblast transferrin-receptor expression to be the result of impaired erythropoietin production and inhibition of its activity by cytokines. However, reduced erythropoietin activity, mostly from reduced production, plays a pivotal role in the pathogenesis of ACD observed in systemic autoimmune diseases (Bertero and Caligaris-Cappio, 1997). Indeed, iron metabolism as well as nitric oxide (NO), which contributes to the regulation of iron cellular metabolism are involved in the pathogenesis of ACD in systemic autoimmune disorders. Inflammatory mediators, particularly the cytokines, are important factors involved in the pathogenesis of the anaemia of chronic disease, as seen in rheumatoid arthritis anaemia (Baer et al., 1990), the cyt okines causing impairment of erythroid progenitor growth and haemoglobin production in developing erythrocytes.           Anaemia is also commonly found in cases of congestive heart failure (CHF), again caused by excessive cytokine production leading to reduced erythropoietin secretion, interference with erythropoietin activity in the bone marrow and reduced iron supply to the bone marrow (Silverberg et al., 2004). However, in the presence of chronic kidney insufficiency, abnormal erythropoietin production in the kidney plays a role in the pathogenesis of anaemia in CHF.           The myelodysplastic syndromes (MDS) are common haematological malignancies affecting mostly the elderly as age-related telomere shortening enhances genomic instability (Rosenfeld and List, 2000). Radiation, smoking and exposure to toxic compounds e.g., pesticides, organic chemicals and heavy metals, are factors promoting the onset of MDS via damage caused to progenitor cells, and, thereby, inducing immune suppression of progenitor cell growth and maturation. TNF- and other pro-apoptotic cytokines could play a central role in the impaired haematopoiesis of MDS (Rosenfeld and List, 2000). Premature intramedullary cell death brought about by excessive apoptosis is another important pathogenetic mechanism in MDS (Aul et al., 1998).           Sickle cell disease (SCD) arising from a point mutation in the ÃŽ ²-globin gene and leading to the expression of haemoglobin S (HbS) is the most common monogenetic disorder worldwide. Chronic intravascular haemolysis and anaemia are some important characteristics of SCD. Intravascular haemolysis causes endothelial dysfunction marked by reduced nitric oxide (NO) bioavailability and NO resistance, leading to acute vasoconstriction and, subsequently, pulmonary hypertension (Gladwin and Kato, 2005).  However, a feature that differentiates SCD from other chronic haemolytic syndromes is the persistent and intense inflammatory condition present in SCD. The primary pathogenetic event in SCD is the intracellular polymerisation or gelation of deoxygenated HbS leading to rigidity in erythrocytes (Wun, 2001). The deformation of erythrocytes containing HbS is dependent on the concentration of haemoglobin in the deoxy conformation (Rodgers et al., 1985). It has been demonstrated that sickle monocytes are activated which, in turn, activate endothelial cells and cause vascular inflammation. The vaso-occlusive processes in SCD involve inflammatory and adhesion molecules such as the cell adhesion molecules (CAM family), which play a role in the firm adhesion of reticulocytes and leukocytes to endothelial cells, and the selectins, which play a role in leukocyte and platelet rolling on the vascular wall (Connes et al., 2008). Thus, inflammation, leucocyte adhesion to vascular endothelium, and subsequent endothelial injury are other crucial factors contributing to the pathogenesis of SCD (Jison et al., 2004). 4. Current therapies for clinical management of sickle cell diseaseincludingacritical appraisal of transfusion Between 1973 and 2003, the average life expectancy of a patient with SCD increased dramatically from a mere 14 years to 50 years thanks to the development of comprehensive care models and painstaking research efforts in both basic sciences especially molecular and genetic studies, and clinical aspects of SCD (Claster and Vichinsky, 2003). The clinical manifestations of SCD are highly variable. Both the phenotypic expression and intensity of the syndrome are vastly different among patients and also vary longitudinally within the same patient (Ballas, 1998). New pathophysiological insights available have enabled treatments to be developed for the recognised haematologic and nonhaematologic abnormalities in SCD (Claster and Vichinsky, 2003). The main goals of SCD treatment are symptom alleviation, crises avoidance and effective management of disease complications. The strategy adopted is primarily palliative in nature, and consists of supportive, symptomatic and preventative approaches to therapy. Symptomatic management includes pain mitigation, management of vasoocclusive crisis, improving chronic haemolytic anaemia, treatment of organ failure associated with the disease, and detection and treatment of pulmonary hypertension (Distenfeld and Woermann, 2009). The preventative strategies include use of prophylactic antibiotics (e.g., penicillin) in children, prophylactic blood transfusion for prevention of stroke in patients especially young children who are at a very high risk of stroke, and treatment with hydroxyurea of patients experiencing frequent acute painful episodes (Ballas, 2002). Currently, curative therapy for sickle cell anaemia is only available through bone marrow and stem cell transplantation. Hematopoietic cell transplantation using stem cells from a matched sibling donor has yielded excellent results in paediatric patients (Krishnamurti, 2007). Curative gene therapy is still at the exploratory stage (Ballas, 2002). Current and potential therapies The potential treatment strategies basically target cellular dehydration, sickle haemoglobin concentrations, endothelial dysfunction, and abnormal coagulation regulation (Claster and Vichinsky, 2003). HbS concentrations are essentially tackled through transfusions while approaches to reduce HbS polymerisation which is the main mechanism for the development of vaso-occlusion include (a) increasing foetal haemoglobin (HbF) concentration using hydroxyurea (Fig. 2), butyrate, or erythropoietin, and (b) preventing sickle cell dehydration using Clotrimazole (Fig. 3) or Mg2+pidolate. Hydroxyurea therapy increases the production of HbF in patients with sickle cell anaemia, and, thereby, inhibits the polymerisation of HbS and alleviates both the haemolytic and vaso-occlusive manifestations of the disease (Goldberg et al., 1990). Recombinant erythropoietin also increases the number of reticulocytes with HbF. Additionally, it has been observed that administration of intravenous recombinant eryt hropoietin with iron supplementation alternating with hydroxyurea enhances HbF levels more than hydroxyurea alone (Rodgers et al., 1993). As SCD is essentially characterized by an abnormal state of endothelial cell activation that is, a state of inflammation, a pharmacologic approach to inhibit endothelial cell activation has proved clinically beneficial (Hebbel and Vercellotti, 1997). Thus, administration of sulfasalazine which is a powerful inhibitor of activation of nuclear factor (NF)-B, the transcription factor promoting expression of genes for a number of pro-adhesive and procoagulant molecules on endothelium to humans has been found to provide transcriptional regulation of SCD at the endothelium level (Solovey et al., 2001). Red blood cell transfusion : a critical appraisal A key therapy that is applied regularly in the clinical management of patients with SCD is packed red blood cell transfusion. RBC transfusion improves the oxygen-carrying capacity which is achieved by enhancing the haemoglobin levels, causes dilution of HbS concentration thereby, reducing blood viscosity and boosting oxygen saturation. Furthermore, RBC transfusion is helpful in suppressing endogenous production of sickle RBCs by augmenting tissue oxygenation ( Josephson et al., 2007). There are two major types of RBC transfusion therapy: intermittent and chronic which are further classified as prophylactic or therapeutic. Intermittent transfusions are generally therapeutic in nature and administered to control acute manifestations of SCD whereas chronic transfusions are performed as general preventative measures to check complications of SCD. RBC transfusion given as a single dose is termed as simple transfusion. Exchange transfusion involves administration of a larger volume of RBCs replacing the patients RBCs that are simultaneously removed. Details of the various types of RBC transfusion and the major clinical indications for the same in SCD patients are listed in Table 1.      SCD (Source: Josephson et al., 2007) Indications for Intermittent transfusions Indications for intermittent transfusions include acute manifestations of SCD, as indicated in Table 1, that require redressal through therapeutic transfusions. However, under certain circumstances intermittent transfusions could be prophylactic such as for instance, when SCD patients are transfused before specific surgeries viz., those related to pregnancy complications or renal failure (Table 1).           Acute Chest Syndrome (ACS) describes a manifestation of SCD in which, due to sickling, infectious and noninfectious pulmonary events are complicated, resulting in a more severe clinical course. The diagnosis is the presence of a new infiltrate on chest radiography that is accompanied by acute respiratory symptoms. ACD accounts for nearly 25% of all deaths from SCD (Vichinsky, 2002). Repeated episodes of ACS are associated with an increased risk of chronic lung disease and pulmonary hypertension (Castro, 1996). The severe pulmonary events occurring in SCD may be precipitated by any trigger of hypoxia (Vichinsky, 2002). Transfusions are very efficacious and provide immediate benefit by reversing hypoxia in ACS. Transfusion of leucocyte-poor packed red cells matched for Rh, C, E, and Kell antigens can curtail antibody formation to below 1% (Vichinsky, 2002). Simple transfusions suffice for less severe cases; however, exchange transfusion is recomm ended to minimise the risk of increased viscosity. Also, chronic transfusion appears promising for prevention of recurrence in selected patients (Styles and Vichinsky, 1994). In a multicentre ACS trial, prophylactic transfusion was found to almost completely eliminate the risk of pulmonary complications (Vichinsky, 2002).           Acute Symptomatic Anaemia arises in SCD as a result of blood loss, increased RBC destruction, suppression of erythropoiesis etc. and is effectively treated with intermittent transfusion of RBCs to relieve symptoms of cardiac and respiratory distress (Josephson et al., 2007).           Aplastic Anaemia is commonly caused in SCD on account of infection of haematopoietic precursors in the bone marrow by Parvovirus B19 leading to a steep fall in RBCs. According to Josephson et al. (2007), therapeutic intermittent transfusion of RBCs is again the recommended first-line of treatment to improve total haemoglobin count and prevent cardiac decompensation. However, in those patients who are prone to fluid overload on account of cardiac or renal dysfunction an alternative transfusion strategy is to remove the whole blood and replace it with packed cells while avoiding the addition of excess volume (Josephson et al., 2007).           Acute Stroke is a high risk especially in paediatric SCD cases because of elevated cerebral flow. Enormous decline in stroke rate have occurred in children receiving intermittent simple transfusion (Adams et al., 1998). However, the identification of the stroke type would be necessary in all SCD patients in order to determine the appropriate treatment approach since the occurrence of infarctive strokes is higher in children as opposed to a higher incidence of haemorrhagic strokes in adults (Adams, 2003). Indications for Chronic Transfusions Prophylactic chronic RBC transfusion every 3 to 4 weeks to maintain HbS levels lower than 30% is crucial for preventing first as well as recurrent strokes in children (Johnson et al., 2007). The transfusions could either be chronic simple transfusion or prophylactic chronic RBC exchange transfusion. Prophylactic chronic transfusions are recommended for patients with chronic renal failure so as to avoid severe symptomatic anaemia and for those patients with SCD undergoing pregnancy with complications. However, prophylactic transfusion is not indicated for SCD patients with normal pregnancy (Tuck et al., 1987). Controversial and indeterminate indications for intermittent or chronic transfusion According to Hankins et al. (2005), chronic transfusion therapy is helpful in reducing the incidence of strokes in children but not the severity of strokes. In the case of acute priapism, improvement in patients has been observed after exchange or simple transfusion (Rifikind et al., 1979). Yet, due to the ASPEN syndrome, transfusion currently is only a second-line therapy in the management of priapism ( Miller et al., 1995).           RBC transfusion is a vital component in the management of symptoms and complications of SCD. It has drastically reduced the morbidity and mortality of SCD. Yet, immune-related effects such as FNHTRs and alloimmunisation to HLAs, and nonimmune-related effects e.g., iron overload and transfusion-transmitted infections are serious adverse effects of the transfusion therapy that need to be attended to in SCD patients receiving transfusion (Johnson et al., 2007). Chronic transfusions could result in an inexorable accumulation of tissue iron that could become fatal if not treated (Cohen, 1987). Excess iron damages the liver, endocrine organs, and heart and may be fatal by adolescence (Engle, 1964). 5. Critical review of thalassemias : (i) Molecular pathogenesis The large number of inherited haemoglobin disorders known today include (a) those related to anomalies in the haemoglobin structure e.g., sickle cell disease, and (b) the thalassemias whose hallmark is globin-chain deficiency of one or other of the globin chains of adult haemoglobin in erythroid cells. ÃŽ ²-Thalassaemias These are a set of genetic disorders inherited as simple codominant traits affecting haemoglobin synthesis. Depending on the haemoglobin chain affected, 2 types of thalassemia are recognised: ÃŽ ±-thalassaemia and ÃŽ ²-thalassaemia. Homozygous ÃŽ ²-thalassaemia is marked by a quantitative deficiency of the ÃŽ ²-globin chains in the erythroid cells. A complete absence of the ÃŽ ²-globin chains occurs in homozygous ÃŽ ²o-thalassaemia whereas in homozygous ÃŽ ²+-thalassaemia the ÃŽ ²-globin chains are present at less than 30% of normal. Accounting for nearly 90% of the cases, ÃŽ ²+-thalassaemia is the most commonly observed form of ÃŽ ²-thalassaemia. The condition is termed thalassaemia major when there is microcytic hypochromic anaemia with severe haemolysis, hepatosplenomegaly, skeletal deformities and iron overload. ÃŽ ²-thalassaemia homozygotes exhibit severe transfusion-dependent anaemia in the very first year of life. Homozygotic individuals having a relatively benign clinical phe notype and surviving with or without transfusion are described as thalassaemia intermedia (Weatherall, 1969). The thalassaemias, thus, encompass a wide gamut of clinical disability from intrauterine death to a mild anaemia with no overt symptoms (Weatherall, 1997b). The coexistence of Î ± -thalassaemia leading to reduction in the synthesis of ÃŽ ±-globin chains, and a genetic predisposition to produce high levels of HbF, could be important factors for the extensive p Causes, Symptoms and Treatments of Anaemia Causes, Symptoms and Treatments of Anaemia 1. Introduction Anaemia is a syndrome characterised by a lack of healthy red blood cells or haemoglobin deficiency in the red blood cells, resulting in inadequate oxygen supply to the tissues. The condition can be temporary, long-term or chronic, and of mild to severe intensity. There are many forms and causes of anaemia. Normal blood consists of three types of blood cells: white blood cells (leucocytes), platelets and red blood cells (erythrocytes). The first generation of erythrocyte precursors in the developing foetus are produced in the yolk sac. They are carried to the developing liver by the blood where they form mature red blood cells that are required to meet the metabolic needs of the foetus. Until the 18th week of gestation, erythrocytes are produced only by liver after which the production shifts to the spleen and the bone marrow. The life of a red blood cell is about 127 days or 4 months (Shemin and Rittenberg, 1946; Kohgo et al., 2008). The main causes of anaemia are blood loss, product ion of too few red blood cells by the bone marrow or a rapid destruction of cells.           Haemoglobin, a protein, present in the red blood cells is involved in the transport of oxygen from the lungs to all the other organs and tissues of the body. Iron is an important constituent of the haemoglobin protein structure which is intimately involved in the transport of oxygen. Anaemia is generally defined as a lower than normal haemoglobin concentration. The normal blood haemoglobin concentration is dependent on age and sex, and, according to the World Health Organisation (WHO) Expert Committee Report, anaemia results when the blood concentration of haemoglobin falls below 130 g/L in men or 120 g/L in non-pregnant women (WHO, 1968). However, the reference range of haemoglobin concentration in blood could vary depending on the ethnicity, age, sex, environmental conditions and food habits of the population analysed. According to Beutler and Warren (2006), more reasonable benchmarks for anaemia are 137 g/L for white men aged between 20 and 60 years and 132 g/L for older men. The value for women of all ages would be 122 g/L. Also, the lower limit of normal of haemoglobin concentrations of African Americans are appreciably lower than that of Caucasians (Beutler and Warren, 2006).           Besides the well recognised iron deficiency anaemia, several inherited anaemias are also known. These are mostly haemoglobinopathies. Adult haemoglobin is a tetrameric haeme-protein. Abnormalities of beta-chain or alpha-chain produce the various medically significant haemoglobinopathies. The variations in amino acid composition induced genetically impart marked differences in the oxygen carrying properties of haemoglobin. Mutations in the haemoglobin genes cause disorders that are qualitative abnormalities in the synthesis of haemoglobin (e.g., sickle cell disease) and some that are quantitative abnormalities that pertain to the rate of haemoglobin synthesis (e.g., the thalassemias) (Weatherall., 1969). In SCD, the missense mutation in the ÃŽ ²-globin gene causes the disorder. The mutation causing sickle cell anemia is a single nucleotide substitution (A to T) in the codon for amino acid 6. The substitution converts a glutamic acid codon (GAG) to a valine codon (GTG). The form of haemoglobin in persons with sickle cell anemia is referred to as HbS. Also, the valine for glutamic acid replacement causes the haemoglobin tetramers to aggregate into arrays upon deoxygenation in the tissues. This aggregation leads to deformation of the red blood cell making it relatively inflexible and restrict its movement in the capillary beds. Repeated cycles of oxygenation and deoxygenation lead to irreversible sickling and clogging of the fine capillaries. Incessant clogging of the capillary beds damages the kidneys, heart and lungs while the constant destruction of the sickled red blood cells triggers chronic anaemia and episodes of hyperbilirubinaemia.           Fanconi anaemia (FA) is an autosomal recessive condition, and the most common type of inherited bone marrow failure syndrome. The clinical features of FA are haematological with aplastic anaemia, myelodysplastic syndrome (MDS), and acute myeloid leukaemia (AML) being increasingly present in homozygotes (Tischkowitz and Hodgson, 2003). Cooleys anaemia is yet another disorder caused by a defect in haemoglobin synthesis.           Autoimmune haemolytic anaemia is a syndrome in which individuals produce antibodies directed against one of their own erythrocyte membrane antigens. The condition results in diminished haemoglobin concentrations on account of shortened red blood cell lifespan (Sokol et al., 1992).           Megaloblastic anaemia is a blood disorder in which anaemia occurs with erythrocytes which are larger in size than normal. The disorder is usually associated with a deficiency of vitamin B12 or folic acid . It can also be caused by alcohol abuse, drugs that impact DNA such as anti-cancer drugs, leukaemia, and certain inherited disorders among others (Dugdale, 2008).           Malaria causes increased deformability of vivax-infected red blood cells (Anstey et al., 2009). Malarial anaemia occurs due to lysis of parasite-infected and non-parasitised erythroblasts as also by the effect of parasite products on erythropoiesis (Ru et al., 2009).           Large amounts of iron are needed for haemoglobin synthesis by erythroblasts in the bone marrow. Transferrin receptor 1 (TfR1) expressed highly in erythroblasts plays an important role in extracellular iron uptake (Kohgo et al., 2008). Inside the erythroblasts, iron transported into the mitochondria gets incorporated into the haeme ring in a multistep pathway. Genetic abnormalities in this pathway cause the phenotype of ringed sideroblastic anemias (Fleming, 2002). The sideroblastic anemias are a heterogeneous group of acquired and inherited bone marrow disorders, characterised by mitochondrial iron overload in developing red blood cells. These conditions are diagnosed by the presence of pathologic iron deposits in erythroblast mitochondria (Bottomley, 2006).  2. Classification of anaemia Anaemia can be generally classified based on the morphology of the red blood cells, the pathogenic spectra or clinical presentation (Chulilla et al., 2009). The morphological classification is based on mean corpuscular volume (MCV) and comprises of microcytic, macrocytic and normocytic anaemia.      (a) Microcytic anaemia refers to the presence of RBCs smaller than normal volume, the reduced MCV ( 15 would probably indicate IDA (Chulilla et al., 2009).           In macrocytic anaemia, erythrocytes are larger (MCV > 98 fL) than their normal volume (MCV = 82-98 fL). Vitamin B12 deficiency leads to delayed DNA synthesis in rapidly growing hematopoietic cells, and can result in macrocytic anemia. Drugs that interfere with nucleic acid metabolism, such as.hydroxyurea increases MCV (> 110 fL) while alcohol induces a moderate macrocytosis (100-110 fL). In the initial stage, most anaemias are normocytic. The causes of normocytic anaemia are nutritional deficiency, renal failure and haemolytic anemia (Tefferi, 2003). The most common normocytic anaemia in adults is anaemia of chronic disease (ACD) (Krantz, 1994). Common childhood normocytic anaemias are, besides iron deficiency anaemia, those due to acute bleeding, sickle cell anemia, red blood cell membrane disorders and current or recent infections especially in the very young (Bessman et al., 1983). Homozygous sickle cell disease is the most common cause of h aemolytic normocytic anemias in children (Weatherall DJ, 1997a).           In practice, the morphological classification is quicker and therefore, more useful as a diagnostic tool. Besides, MCV is also closely linked to mean corpuscular haemoglobin (MCH), which denotes mean haemoglobin per erythrocyte expressed in picograms (Chulilla et al., 2009). Thus, MCV and MCH decrease simultaneously in microcytic, hypochromic anemia and increase together in macrocytic, hyperchromic anemia.           Pathogenic classification of anaemia is based on the production pattern of RBC: whether anaemia is due to inadequate production or loss of erythrocytes caused by bleeding or haemolysis. This approach is useful in those cases where MCV is normal. Pathogenic classification is also essential for proper recognition of the mechanisms involved in the genesis of anaemia. Based on the pathogenic mechanisms, anaemia is further divided into two types namely, (i) hypo-regenerative in which the bone marrow production of erythrocytes is decreased because of impaired function, decreased number of precursor cells, reduced bone marrow infiltration, or lack of nutrients; and (ii) regenerative: when bone marrow upregulates the production of erythrocytes in response to the low erythrocyte mass (Chulilla et al., 2009). This is typified by increased generation of erythropoietin in response to lowered haemoglobin concentration, and also reflects a loss of erythrocyt es, due to bleeding or haemolysis. The reticulocyte count is typically higher.           Sickle cell disease is characterised by sickled red cells. The first report of SCD was published a century ago noting the presence of peculiar elongated cells in blood by James Herrick, an American physician (1910). Pauling et al. (1949) described it as a molecular disease. The molecular nature of sickle haemoglobin (Hb S) in which valine is substituted for glutamic acid at the sixth amino acid position in the beta globin gene reduces the solubility of Hb, causing red cells to sickle (Fig. 1). Sickling of cells occurs at first reversibly, then finally as a state of permanent distortion, when cells containing HbS and inadequate amounts of other haemoglobins including foetal haemoglobin, which retards sickling, become deoxygenated (Bunn, 1997). The abnormal red cells break down, leading to anaemia, and clog blood vessels with aggregates, leading to recurrent episodes of severe pain and multiorgan ischaemic damage (Creary et al., 2007). The high levels of inflammatory cytokines in SCD may promote retention of iron by macrophage/reticuloendothelial cells and/or renal cells. SCD care commonly depends on transfusion that results in iron overload (Walter et al., 2009). 3. Pathogenesis of anaemia Anaemia is a symptom , or a syndrome, and not a disease (Chulilla et al., 2009). Several types of anaemia have been recognised, the pathogenesis of each being unique. Iron deficiency anaemia (IDA) is the most common type of anaemia due to nutritional causes encountered worldwide (Killip et al., 2008). Iron is one of the essential micronutrients required for normal erythropoietic function While the causes of iron deficiency vary significantly depending on chronological age and gender, IDA can reduce work capacity in adults (Haas Brownlie, 2001) and affect motor and mental development in children (Halterman et al., 2001). The metabolism of iron is uniquely controlled by absorption rather than excretion (Siah et al., 2006). Iron absorption typically occurring in the duodenum accounts for only 5 to 10 per cent of the amount ingested in homoeostatis. The value decreases further under conditions of iron overload, and increases up to fivefold under conditions of iron depletion (Killip et al., 2008). Iron is ingested as haem iron (10%) present in meat, and as non-haem ionic form iron (90%) found in plant and dairy products. In the absence of a regulated excretion of iron through the liver or kidneys, the only way iron is lost from the body is through bleeding and sloughing of cells. Thus, men and non-menstruating women lose about 1 mg of iron per day while menstruating women could normally lose up to 1.025 mg of iron per day (Killip et al., 2008). The requirements for erythropoiesis which are typically 20-30 mg/day are dependent on the internal turnover of iron (Munoz et al., 2009) For example, the amount of iron required for daily production of 300 billion RBCs (20-30 mg) is provided mostly by recycling iron by macrophages (Andrews, 1999).           Iron deficiency occurs when the metabolic demand for iron exceeds the amount available for absorption through consumption. Deficiency of nutritional intake of iron is important, while abnormal iron absorption due to hereditary or acquired iron-refractory iron deficiency anemia (IRIDA) is another important cause of unexplained iron deficiency. However, IDA is commonly attributed to blood loss e.g., physiological losses in women of reproductive age. It might also represent occult bleeding from the gastrointestinal (GI) tract generally indicative of malignancy (Hershko and Skikne, 2009).           Iron absorption and loss play an important role in the pathogenesis and management of IDA. Human iron disorders are necessarily disorders of iron balance or iron distribution. Iron homeostasis involves accurate control of intestinal iron absorption, efficient utilisation of iron for erythropoiesis, proper recycling of iron from senescent erythrocytes, and regulated storage of iron by hepatocytes and macrophages (Andrews, 2008). Iron deficiency is largely acquired, resulting from blood loss (e.g., from intestinal parasitosis), from inadequate dietary iron intake, or both. Infections, for example, with H pylori, can lead to profound iron deficiency anemia without significant bleeding. Genetic defects can cause iron deficiency anaemia. Mutations in the genes encoding DMT1 (SLC11A2) and glutaredoxin 5 (GLRX5) lead to autosomal recessive hypochromic, microcytic anaemia (Mims et al., 2005). Transferrin is a protein that keeps iron nonreactive in the circulation, and delivers iron to cells possessing specific transferrin receptors such as TFR1 which is found in largest amounts on erythroid precursors. Mutations in the TF gene leading to deficiency of serum transferrin causes disruption in the transfer of iron to erythroid precursors thereby producing an enormous increase in intestinal iron absorption and consequent tissue iron deposition (Beutler et al., 2000). Quigley et al. (2004) found a haem exporter, FLVCR, which appears to be necessary for normal erythroid development. Inactivation of FLVCR gene after birth in mice led to severe macrocytic anaemia, indicating haem export to be important for normal erythropoiesis.           The anaemia of chronic disease (ACD) found in patients with chronic infectious, inflammatory, and neoplastic disorders is the second most frequently encountered anaemia after iron-deficiency anaemia. It is most often a normochromic, normocytic anaemia that is primarily caused by an inadequate production of red cells, with low reticulocyte production (Krantz, 1994). The pathogenesis of ACD is unequivocally linked to increased production of the cytokines including tumour necrosis factor, interleukin-1, and the interferons that mediate the immune or inflammatory response. The various processes leading to the development of ACD such as reduced life span of red cells, diminished erythropoietin effect on anaemia, insufficient erythroid colony formation in response to erythropoietin, and impaired bioavailability of reticuloendothelial iron stores appear to be caused by inflammatory cytokines (Means, 1996;2003). Although iron metabolism is characterist ically impaired in ACD, it may not play a key role in the pathogenesis of ACD (Spivak, 2002). Neither is the lack of available iron central to the pathogenesis of the syndrome, according to Spivak (2002), who found reduced iron absorption and decreased erythroblast transferrin-receptor expression to be the result of impaired erythropoietin production and inhibition of its activity by cytokines. However, reduced erythropoietin activity, mostly from reduced production, plays a pivotal role in the pathogenesis of ACD observed in systemic autoimmune diseases (Bertero and Caligaris-Cappio, 1997). Indeed, iron metabolism as well as nitric oxide (NO), which contributes to the regulation of iron cellular metabolism are involved in the pathogenesis of ACD in systemic autoimmune disorders. Inflammatory mediators, particularly the cytokines, are important factors involved in the pathogenesis of the anaemia of chronic disease, as seen in rheumatoid arthritis anaemia (Baer et al., 1990), the cyt okines causing impairment of erythroid progenitor growth and haemoglobin production in developing erythrocytes.           Anaemia is also commonly found in cases of congestive heart failure (CHF), again caused by excessive cytokine production leading to reduced erythropoietin secretion, interference with erythropoietin activity in the bone marrow and reduced iron supply to the bone marrow (Silverberg et al., 2004). However, in the presence of chronic kidney insufficiency, abnormal erythropoietin production in the kidney plays a role in the pathogenesis of anaemia in CHF.           The myelodysplastic syndromes (MDS) are common haematological malignancies affecting mostly the elderly as age-related telomere shortening enhances genomic instability (Rosenfeld and List, 2000). Radiation, smoking and exposure to toxic compounds e.g., pesticides, organic chemicals and heavy metals, are factors promoting the onset of MDS via damage caused to progenitor cells, and, thereby, inducing immune suppression of progenitor cell growth and maturation. TNF- and other pro-apoptotic cytokines could play a central role in the impaired haematopoiesis of MDS (Rosenfeld and List, 2000). Premature intramedullary cell death brought about by excessive apoptosis is another important pathogenetic mechanism in MDS (Aul et al., 1998).           Sickle cell disease (SCD) arising from a point mutation in the ÃŽ ²-globin gene and leading to the expression of haemoglobin S (HbS) is the most common monogenetic disorder worldwide. Chronic intravascular haemolysis and anaemia are some important characteristics of SCD. Intravascular haemolysis causes endothelial dysfunction marked by reduced nitric oxide (NO) bioavailability and NO resistance, leading to acute vasoconstriction and, subsequently, pulmonary hypertension (Gladwin and Kato, 2005).  However, a feature that differentiates SCD from other chronic haemolytic syndromes is the persistent and intense inflammatory condition present in SCD. The primary pathogenetic event in SCD is the intracellular polymerisation or gelation of deoxygenated HbS leading to rigidity in erythrocytes (Wun, 2001). The deformation of erythrocytes containing HbS is dependent on the concentration of haemoglobin in the deoxy conformation (Rodgers et al., 1985). It has been demonstrated that sickle monocytes are activated which, in turn, activate endothelial cells and cause vascular inflammation. The vaso-occlusive processes in SCD involve inflammatory and adhesion molecules such as the cell adhesion molecules (CAM family), which play a role in the firm adhesion of reticulocytes and leukocytes to endothelial cells, and the selectins, which play a role in leukocyte and platelet rolling on the vascular wall (Connes et al., 2008). Thus, inflammation, leucocyte adhesion to vascular endothelium, and subsequent endothelial injury are other crucial factors contributing to the pathogenesis of SCD (Jison et al., 2004). 4. Current therapies for clinical management of sickle cell diseaseincludingacritical appraisal of transfusion Between 1973 and 2003, the average life expectancy of a patient with SCD increased dramatically from a mere 14 years to 50 years thanks to the development of comprehensive care models and painstaking research efforts in both basic sciences especially molecular and genetic studies, and clinical aspects of SCD (Claster and Vichinsky, 2003). The clinical manifestations of SCD are highly variable. Both the phenotypic expression and intensity of the syndrome are vastly different among patients and also vary longitudinally within the same patient (Ballas, 1998). New pathophysiological insights available have enabled treatments to be developed for the recognised haematologic and nonhaematologic abnormalities in SCD (Claster and Vichinsky, 2003). The main goals of SCD treatment are symptom alleviation, crises avoidance and effective management of disease complications. The strategy adopted is primarily palliative in nature, and consists of supportive, symptomatic and preventative approaches to therapy. Symptomatic management includes pain mitigation, management of vasoocclusive crisis, improving chronic haemolytic anaemia, treatment of organ failure associated with the disease, and detection and treatment of pulmonary hypertension (Distenfeld and Woermann, 2009). The preventative strategies include use of prophylactic antibiotics (e.g., penicillin) in children, prophylactic blood transfusion for prevention of stroke in patients especially young children who are at a very high risk of stroke, and treatment with hydroxyurea of patients experiencing frequent acute painful episodes (Ballas, 2002). Currently, curative therapy for sickle cell anaemia is only available through bone marrow and stem cell transplantation. Hematopoietic cell transplantation using stem cells from a matched sibling donor has yielded excellent results in paediatric patients (Krishnamurti, 2007). Curative gene therapy is still at the exploratory stage (Ballas, 2002). Current and potential therapies The potential treatment strategies basically target cellular dehydration, sickle haemoglobin concentrations, endothelial dysfunction, and abnormal coagulation regulation (Claster and Vichinsky, 2003). HbS concentrations are essentially tackled through transfusions while approaches to reduce HbS polymerisation which is the main mechanism for the development of vaso-occlusion include (a) increasing foetal haemoglobin (HbF) concentration using hydroxyurea (Fig. 2), butyrate, or erythropoietin, and (b) preventing sickle cell dehydration using Clotrimazole (Fig. 3) or Mg2+pidolate. Hydroxyurea therapy increases the production of HbF in patients with sickle cell anaemia, and, thereby, inhibits the polymerisation of HbS and alleviates both the haemolytic and vaso-occlusive manifestations of the disease (Goldberg et al., 1990). Recombinant erythropoietin also increases the number of reticulocytes with HbF. Additionally, it has been observed that administration of intravenous recombinant eryt hropoietin with iron supplementation alternating with hydroxyurea enhances HbF levels more than hydroxyurea alone (Rodgers et al., 1993). As SCD is essentially characterized by an abnormal state of endothelial cell activation that is, a state of inflammation, a pharmacologic approach to inhibit endothelial cell activation has proved clinically beneficial (Hebbel and Vercellotti, 1997). Thus, administration of sulfasalazine which is a powerful inhibitor of activation of nuclear factor (NF)-B, the transcription factor promoting expression of genes for a number of pro-adhesive and procoagulant molecules on endothelium to humans has been found to provide transcriptional regulation of SCD at the endothelium level (Solovey et al., 2001). Red blood cell transfusion : a critical appraisal A key therapy that is applied regularly in the clinical management of patients with SCD is packed red blood cell transfusion. RBC transfusion improves the oxygen-carrying capacity which is achieved by enhancing the haemoglobin levels, causes dilution of HbS concentration thereby, reducing blood viscosity and boosting oxygen saturation. Furthermore, RBC transfusion is helpful in suppressing endogenous production of sickle RBCs by augmenting tissue oxygenation ( Josephson et al., 2007). There are two major types of RBC transfusion therapy: intermittent and chronic which are further classified as prophylactic or therapeutic. Intermittent transfusions are generally therapeutic in nature and administered to control acute manifestations of SCD whereas chronic transfusions are performed as general preventative measures to check complications of SCD. RBC transfusion given as a single dose is termed as simple transfusion. Exchange transfusion involves administration of a larger volume of RBCs replacing the patients RBCs that are simultaneously removed. Details of the various types of RBC transfusion and the major clinical indications for the same in SCD patients are listed in Table 1.      SCD (Source: Josephson et al., 2007) Indications for Intermittent transfusions Indications for intermittent transfusions include acute manifestations of SCD, as indicated in Table 1, that require redressal through therapeutic transfusions. However, under certain circumstances intermittent transfusions could be prophylactic such as for instance, when SCD patients are transfused before specific surgeries viz., those related to pregnancy complications or renal failure (Table 1).           Acute Chest Syndrome (ACS) describes a manifestation of SCD in which, due to sickling, infectious and noninfectious pulmonary events are complicated, resulting in a more severe clinical course. The diagnosis is the presence of a new infiltrate on chest radiography that is accompanied by acute respiratory symptoms. ACD accounts for nearly 25% of all deaths from SCD (Vichinsky, 2002). Repeated episodes of ACS are associated with an increased risk of chronic lung disease and pulmonary hypertension (Castro, 1996). The severe pulmonary events occurring in SCD may be precipitated by any trigger of hypoxia (Vichinsky, 2002). Transfusions are very efficacious and provide immediate benefit by reversing hypoxia in ACS. Transfusion of leucocyte-poor packed red cells matched for Rh, C, E, and Kell antigens can curtail antibody formation to below 1% (Vichinsky, 2002). Simple transfusions suffice for less severe cases; however, exchange transfusion is recomm ended to minimise the risk of increased viscosity. Also, chronic transfusion appears promising for prevention of recurrence in selected patients (Styles and Vichinsky, 1994). In a multicentre ACS trial, prophylactic transfusion was found to almost completely eliminate the risk of pulmonary complications (Vichinsky, 2002).           Acute Symptomatic Anaemia arises in SCD as a result of blood loss, increased RBC destruction, suppression of erythropoiesis etc. and is effectively treated with intermittent transfusion of RBCs to relieve symptoms of cardiac and respiratory distress (Josephson et al., 2007).           Aplastic Anaemia is commonly caused in SCD on account of infection of haematopoietic precursors in the bone marrow by Parvovirus B19 leading to a steep fall in RBCs. According to Josephson et al. (2007), therapeutic intermittent transfusion of RBCs is again the recommended first-line of treatment to improve total haemoglobin count and prevent cardiac decompensation. However, in those patients who are prone to fluid overload on account of cardiac or renal dysfunction an alternative transfusion strategy is to remove the whole blood and replace it with packed cells while avoiding the addition of excess volume (Josephson et al., 2007).           Acute Stroke is a high risk especially in paediatric SCD cases because of elevated cerebral flow. Enormous decline in stroke rate have occurred in children receiving intermittent simple transfusion (Adams et al., 1998). However, the identification of the stroke type would be necessary in all SCD patients in order to determine the appropriate treatment approach since the occurrence of infarctive strokes is higher in children as opposed to a higher incidence of haemorrhagic strokes in adults (Adams, 2003). Indications for Chronic Transfusions Prophylactic chronic RBC transfusion every 3 to 4 weeks to maintain HbS levels lower than 30% is crucial for preventing first as well as recurrent strokes in children (Johnson et al., 2007). The transfusions could either be chronic simple transfusion or prophylactic chronic RBC exchange transfusion. Prophylactic chronic transfusions are recommended for patients with chronic renal failure so as to avoid severe symptomatic anaemia and for those patients with SCD undergoing pregnancy with complications. However, prophylactic transfusion is not indicated for SCD patients with normal pregnancy (Tuck et al., 1987). Controversial and indeterminate indications for intermittent or chronic transfusion According to Hankins et al. (2005), chronic transfusion therapy is helpful in reducing the incidence of strokes in children but not the severity of strokes. In the case of acute priapism, improvement in patients has been observed after exchange or simple transfusion (Rifikind et al., 1979). Yet, due to the ASPEN syndrome, transfusion currently is only a second-line therapy in the management of priapism ( Miller et al., 1995).           RBC transfusion is a vital component in the management of symptoms and complications of SCD. It has drastically reduced the morbidity and mortality of SCD. Yet, immune-related effects such as FNHTRs and alloimmunisation to HLAs, and nonimmune-related effects e.g., iron overload and transfusion-transmitted infections are serious adverse effects of the transfusion therapy that need to be attended to in SCD patients receiving transfusion (Johnson et al., 2007). Chronic transfusions could result in an inexorable accumulation of tissue iron that could become fatal if not treated (Cohen, 1987). Excess iron damages the liver, endocrine organs, and heart and may be fatal by adolescence (Engle, 1964). 5. Critical review of thalassemias : (i) Molecular pathogenesis The large number of inherited haemoglobin disorders known today include (a) those related to anomalies in the haemoglobin structure e.g., sickle cell disease, and (b) the thalassemias whose hallmark is globin-chain deficiency of one or other of the globin chains of adult haemoglobin in erythroid cells. ÃŽ ²-Thalassaemias These are a set of genetic disorders inherited as simple codominant traits affecting haemoglobin synthesis. Depending on the haemoglobin chain affected, 2 types of thalassemia are recognised: ÃŽ ±-thalassaemia and ÃŽ ²-thalassaemia. Homozygous ÃŽ ²-thalassaemia is marked by a quantitative deficiency of the ÃŽ ²-globin chains in the erythroid cells. A complete absence of the ÃŽ ²-globin chains occurs in homozygous ÃŽ ²o-thalassaemia whereas in homozygous ÃŽ ²+-thalassaemia the ÃŽ ²-globin chains are present at less than 30% of normal. Accounting for nearly 90% of the cases, ÃŽ ²+-thalassaemia is the most commonly observed form of ÃŽ ²-thalassaemia. The condition is termed thalassaemia major when there is microcytic hypochromic anaemia with severe haemolysis, hepatosplenomegaly, skeletal deformities and iron overload. ÃŽ ²-thalassaemia homozygotes exhibit severe transfusion-dependent anaemia in the very first year of life. Homozygotic individuals having a relatively benign clinical phe notype and surviving with or without transfusion are described as thalassaemia intermedia (Weatherall, 1969). The thalassaemias, thus, encompass a wide gamut of clinical disability from intrauterine death to a mild anaemia with no overt symptoms (Weatherall, 1997b). The coexistence of Î ± -thalassaemia leading to reduction in the synthesis of ÃŽ ±-globin chains, and a genetic predisposition to produce high levels of HbF, could be important factors for the extensive p
Friday, January 17, 2020
The Aircraft Collision Issues
On March 27, 1977 at 1706:52 G. M. T. A KLM 747 collided with a Pan Am 747 in dense fog on runway 30 at Los Rodeos Airport in the Spanish Canary Islands. KLM flight 4805 was a 747-206B with serial number PH-BUF. Pan Am flight 1736 was a 747-121 with serial number N736PA. Both aircraft were properly maintained and airworthy according to the regulations of the country of registration. All crew members of both aircraft were properly certified and current for their particular crew member positions on the Boeing 747. The KLM captain had 11,700 hrs. With 1,545 of those hours on the 747. The First officer had a total of 9,200 hours at the time of the accident with only 95 hours on the 747. The flight engineer had 17,031 hours with 543 hours on the 747. The Pan Am captain had 21,043 total with 584 hours on the 747. His co-pilot had 10,800 hours with 2,796 hours on the 747. The flight engineer had 15,210 hours total flight time with 559 hours on the 747. KLM 4805 was a charter flight from Amsterdam, Netherlands to Las Palmas, Canary Islands on behalf of Holland international Travel Group. Pan Am 1736 was also a charter flight to Las Palmas originating in Los Angeles, California the previous afternoon with a stop over and crew change at New York (JFK). The two aircraft involved in the accident were diverted to Los Rodeos because of a terrorist bomb explosion at Las Palmas Airport. There was a threat of another bomb so for security reasons no one could land there. Upon arrival at Los Rodeos several other diverted airliners were already on the ground waiting to go to Las Palmas. The Pan Am parked next to the KLM. The captain of the KLM was constantly on the radio trying to find out when the airport would reopen. He was concerned that he and his flight crew were going to run out of duty time. He decided to get fuel while he was waiting in order to avoid the servicing delay that would be awaiting them at Las Palmas. Las Palmas was reopened while the KLM was in the middle of refueling. The Pan Am was ready to depart but had to wait for the KLM to finish refueling because they couldn't taxi around them. Both aircraft were given instruction to use the active runway 30 as a taxiway because aircraft were parked on the paralleling taxiway. The KLM taxied to the end of the runway and made a 180 degree turn to align itself for takeoff. The Pan Am lagged behind because a blanket of fog surrounded them making it difficult to find their turn off. The Pan Am crew was unsure which taxiway they were to get on. The controller told the Pan Am to exit at the 3rd taxiway. This didn't make sense to them because they would have needed to make a 135 degree turn. The fourth taxiway was only 45 degrees. As the KLM 747 completed its turn and the pre-takeoff checklists were complete the captain started adding power for take off. The first officer noticed this and said, â€Å"Wait a minute, we don't have an ATC clearance. The captain held the brakes and said, â€Å"No†¦ I know that. Go ahead ask. †The KLM requested ATC clearance. The tower read them their departure clearance but did not clear them for takeoff. The KLM captain advanced the throttles again as the first officer read back the clearance. The KLM first officer told ATC they were, â€Å"at takeoff. †The Pan Am heard this and said that they will report when clear the runway. They understood â€Å"at takeoff†to mean at takeoff position. The KLM second officer questioned the captain, â€Å"Did he not clear the runway – that Pan American? The captain said, â€Å"Yes, he did. †Moments later the Pan Am first officer noticed the takeoff lights of the KLM approaching fast. He shouted, â€Å"Get off, Get off! †The captain put in full power and tried to drive the airplane into the grass. The pilots on the KLM noticed the Pan Am slewing across the runway after V1 was called. The captain knew that there wasn't enough room to stop so he over-rotated causing the tail of his aircraft to strike the runway in a shower of sparks. But lift the KLM did – just before reaching the Pan AM. The KLM smashed (with a nose up attitude) into the port side of the Pan Am 747. The KLM continued airborne down the runway another 450 meters past the point of collision where it crashed with full fuel and burned killing all 248 souls on board. The Pan Am was soon engulfed in flames. The impact tore off the top of the Pan Am 747 fuselage from the tail to the back of the cockpit. The Pan Am with its entire top fuselage having been carried away by the KLM, caught fire killing 326 of the 396 souls on board. No one in the tower saw the accident because of the fog. Other aircraft waiting on the taxiway saw a series of explosions and reported them to the tower. Emergency crews were immediately notified. The dense fog delayed the effort of the emergency crews to find the planes. The firemen didn't realize that there were two aircraft involved until they were at the wreckage of the KLM and the fog cleared a little bit to see the Pan AM on fire further down the runway. The main cause of this accident was that the KLM captain took off without clearance. The captain also failed to heed the towers instruction to â€Å"standby for takeoff. Finally, the captain did not abandon the takeoff when it became apparent that the Pan Am was still on the runway. He was obviously in a hurry due to the fact that he and his crew might run out of flight time. They had been flying for a long time and probably had get-homeitis. KLM 4805 was nearing the takeoff minimums perscribed for KLM because of the thick fog which put more pressure on the Captain to takeoff. He didn't want to have to leave the aircraft over night and wait for a change of crew because that would inconvienience everyone and cost money. It is also interesting to note that a procedure error took place. This experienced captain should know the difference between being given takeoff clearance and being given a route of flight clearance. The fact of the matter is that the captain had been spending most of his time for the past ten years as a training captain at Schiphol Airport. â€Å"This tended to reduce his day to day familiarity with route flying and its procedures†(Job 177). This idea then leads to the probability that there was a miscommunication between the tower and the KLM. The tower controller and the Pan Am transmitted over each other information that would have prevented the accident. The tower said, â€Å"OK†¦ standby for takeoff†¦ I will call you. †The Pan Am said, â€Å"We are still taxiing down the runway! †The KLM only heard the controller say, â€Å"OK. †The first officer on the KLM declined to take their clearance while they were taxiing because they were too busy doing their pre-takeoff checklists. They instead received their clearance as they lined up for takeoff. This led the captain to believe that the airway clearance they were given also counted as their clearance to takeoff. The first officer already told him once that they didn't have their clearance. He wasn't about to do it again out of fear because the first officer felt resignation. He thought that this captain gave him his 747 rating only 95 flight hours ago and he was in no place to second guess him. The crew of the KLM had poor situational awareness because they turned a deaf ear to the conversations between ATC and the Pan Am crew. They never heard the tower tell Pan Am to report when they were clear. This is proven by the emphatic response to the flight engineers query as to whether or not the Pan Am was cleared of the runway. The captain and first officer said, â€Å"Yes, he's cleared! †The Pan Am crew contributed to the accident by missing their assigned taxiway. If they had turned at the assigned taxiway they would have been off the runway in time. There are several contributing factors to the Tenerife disaster that could have been avoided. If any one of these mistakes didn't happen, the accident would have never happened. If the Pan Am crew had better charts and diagrams of the Los Rodeos Airport, they would have never missed their turn off. The Pan Am would have been off the runway in plenty of time. If the KLM crew was not in such a hurry, the captain would not have commenced takeoff roll before distinct clearance to takeoff. If KLM had Cockpit Resource Management training, the first officer would not have felt intimidated by the captain. He would have corrected the captain again for trying to takeoff without adequate clearance. The captain would have been trained to accept the input of his fellow crew members. If the Pan Am first officer and the tower had not stepped on eachother over the radio, the KLM would have heard both warnings that would have prevented the accident.
Thursday, January 9, 2020
Manifest Destiny, By John C. Sullivan - 1556 Words
1. (Intro) since July 4th 1776 the great country we call the United States has been growing. It started small; just a few immigrants seeking a new world for religious freedoms, and has grown into a world power. It was not an easy journey though, our country experienced many struggles along the way: political disagreements over land, wars, Indian, and technological blocks. As a country we have been very resourceful; throughout history we have come together, explored new land, made monumental changes in technologies, and our thought processes. Once a country of only thirteen colonies, we have gone through great westward expansion to become a united nation of fifty states. 2. (Manifest Destiny) with this great expansion came the idea of manifest Destiny. Manifest destiny is based on the concepts that Americans were destined to expand their boundaries over vast amounts of land. It was an idea introduced by John C. Sullivan. Many of the United States people were immigrants that came to the United States in search for new beginning. The idea of manifest destiny played a great roll in the expansion of the country to the west. The government gave land to the new people to start and start colonizing. With this colonization our countries wealth and power increased .it was believed that to be a successful country we not only needed to be politically and militarily strong but also have a large land mass. Power came along with the size of your country.it was believed that to sustainShow MoreRelatedAp American History - by: Alberto Alonso937 Words  | 4 PagesAmerica because they believed in Manifest Destiny (an idea during the 19th century in which people be lieved that America should expand over the entirety of North America) or because they feared that Texas was an independent state, even the Gold Rush in California (1848-1855) contributed to the expansion of America. Even though â€Å"the opponents of the annexation of Texas and the Mexican War attacked slavery as the root cause of expansion†the idea of Manifest Destiny, fear, and the Gold Rush were otherRead MoreThe Civil War And The American War1318 Words  | 6 PagesThe question of what caused the Civil War is debatable because there are several events that may have influenced the war such as the Western Expansion, Manifest Destiny and the Mexican-American War. The war also stems from slavery, the North and South basically fought over whether or not slavery should be permitted. Another point that may have influenced the Civil War is the economic and social structure of the country, which also falls under slavery because the South main source of income was slaveryRead M oreManifest Destiny And The American Nation2335 Words  | 10 Pages Manifest Destiny is the term used by early Americans to describe the belief of the God given opportunity to spread and expand westward towards the pacific ocean. Many settlers believed that God himself blessed the expansion of the American nation. Beginning with the Louisiana Purchase in 1803, Manifest Destiny brought with it not only territorial acquisitions, but also conflicts over the spread of slavery. Southerners wanting to find more land for cultivation, were led to the desire of acquiringRead MoreThe Causes And Factors Of The Mexican American War1860 Words  | 8 Pagesforefront of national politics, whether we consider the Missouri Compromise and the balance created of one state slave, and one state free, or the gag rule in Congress which restricted the discussion of the very issue. However, in the Presidencies of John Tyler and James Polk the main topic accompanying slavery was its expansion and none illustrated this more than Texas. Texas although formally a state of M exico, starting at the beginning of the century was being flooded by migrants from the South,Read MoreEssay on American Imperialism in the Philippines3614 Words  | 15 Pages181). The Monroe Doctrine and the Manifest Destiny stated Americas philosophies regarding foreign policy. The Monroe Doctrine (1823), crafted by President Monroe and Secretary of State John Quincy Adams, was a statement of Americas foreign policy. It warned Europe to stay out of the Western Hemisphere. Monroe particularly did not want Spain to attempt to reacquire its former colonies that declared their independence (Monroe). The idea of Manifest Destiny stemmed in part from the ideas of theRead MoreComing Of The Civil War1265 Words  | 6 Pagesjoin, since the line went right through the middle of it. Another major addition to the Union was the annexation of Texas in 1845; the Americans believed in the theory of manifest destiny (Doc D)- that they, as white people, were destined to expand across the continent at whatever cost. This term was coined by John L. O Sullivan in his essay titled Annexation that encouraged the US to annex Texas. This was a widely debated topic because Texas would be coming in as a slave state, which the NorthRead More Western Expansion Essay4115 Words  | 17 Pages(1817), Alabama (1819), Maine (1820) and Missouri (1821). By the 1830s, the frontier line had been carried to Iowa, Missouri and Arkansas-about one-third of the way across the continent. By the 1840s, the expansionist policy, typified by the Manifest Destiny doctrine, became very strong with many sections willin g to go to war to acquire more land. Slavery became a bone of contention between the Northern and southern states with the control of the senate in question. The South wanted expansion toRead MoreAPUSH Out of Many Chapter 14 notes2593 Words  | 11 Pagesreinforced sense of pioneering ppl-1890s, Frederick Jackson Turner claimed expansion formed A. Into adventurous,optimisticdemocratic(venture). Manifest Destiny, an Expansionist Ideology: 1.Manifest destiny provided rationale that A. Expansion across continent inevitablyordained by God to bring A.democracy to backward ppl(N.AMexican)-first expressed by John O’Sullivan,1845-summed up nation pride(businesstransportation)missionary zealracist-challenged B. In particular. 2.After Panic of 1837, moreRead MoreAmerican Revolution and Study Guide Essay example5377 Words  | 22 PagesGuide â€Å"Settling the Northern Colonies†1. Compare and contrast the motives of the their founders, religious and social orientation, economic pursuits, and political developments of TWO of the early colonial settlement areas: a. South b. Middle c. New England (30 pts) 2. Some historians have argued the Puritanism was especially suited for life in the wilderness of 17th century America. Do you agree or disagree? Explain (10pts) 3. To what extent had the Massachusetts Bay colonists endorsedRead MoreRosalind Krauss - Photographys Discursive Spaces9350 Words  | 38 Pagesdepictions. It began to internalize the space of exhibition Fig, 3 Samuel Bourne, A Road Lined with Poplars, Kashmir, 1863-70, albumen-silver print from a glass negative, 85/1a X 1I, Collection, Paul F. Walter, New York. P F* 7 - . 3 . I T, r C Y fi 4 Fig. 4 Auguste Salzmann, Jerusalem, The Temple Wall, West Side, 1853-54, salt print from a paper negative, 93/~ax %, Collection, The Museum of Modern Art, New York, Purchase. -the wall--and to represent it. diagonal ordering of the surface
Wednesday, January 1, 2020
Language Arts Warm-Ups for Classroom Engagement
Just as a physical workout needs a solid warm-up for peak performance, warm-up exercises at the start of any class prime students to begin learning. Language arts warm-ups focus on grammar and composition with quick activities to encourage the creative flow. Grab your students attention by engaging them with a stimulating task related to the days lesson. You can introduce it on the whiteboard or with a hard copy placed on everyones desk, but make sure they can get started immediately upon their arrival. Language arts warm-ups can review previously covered material or provide a preview of information to come. They should be quick, fun and designed for student success, such as the examples here. Identifying Adverb Clauses Adverbs modify other words, often verbs but also adjectives and other adverbs, by answering when, where and how. Adverbs may come in dependent clauses, or groups of words, making them a bit harder to identify. Welcome your language arts students to class by asking them to identify the adverb clauses in some recognizable proverbial sayings. Finding Indirect Objects Indirect objects receive or benefit from the action of a verb, but they dont always jump out of a sentence the way direct objects do. Exercises in finding indirect objects get students thinking beyond the easy answers, so warming up with an activity based on indirect objects should make their brains more limber and ready to receive new information. Uncovering Verbals Verbs sometimes stand in as other parts of speech. Collectively called verbals, verbs in use as participles, gerunds, and infinitives may be part of a phrase that includes related modifiers, objects, and complements. Task students with identifying these undercover verbs and revealing their actual identities for a fun way to engage your grammar sleuths. Practicing With Participles and Participial Phrases Building on the identification of verbals, an activity designed to further highlight the role of participles and participial phrases  when verbs become adjectives  sparks recognition that things may not always be as they seem. This useful concept for many language arts topics also translates to most other academic subjects as well. Differentiating Independent and Dependent Clauses A first glance, independent and dependent clauses appear the same. Both contain subjects and verbs, but only independent clauses can stand alone as a sentence. Start class with this exercise to remind students that rote answers rarely work in language arts and encourage them to use their critical thinking skills. Distinguishing Complete Sentences From Sentence Fragments Complete sentences can contain only one word, while sentence fragments may run on for several lines of text. Get students in the mood for grammar with a fun exercise challenging them to turn fragments into full sentences with the addition of a predicate. This activity promotes the development of complete thoughts. Remedying Run-On Sentences Run-on sentences result from missing conjunctions or punctuation. Starting class with an exercise in correcting run-on sentences prompts students to pay attention to the details. This makes a good opener for lessons on composition and creative writing.
Subscribe to:
Posts (Atom)