Hemolytic Anemia Chapter 9-10 PDF

11/13/2023 Hemolytic Anemia Chapter 9 & 10 Week 12 Rania Abu Seir, Ph. D. Associate Professor of Hematology...

11/13/2023 Hemolytic Anemia Chapter 9 & 10 Week 12 Rania Abu Seir, Ph. D. Associate Professor of Hematology Clinical Hematology I (0202306) Harmening DM. Clinical Hematology & Fundamentals of Hemostasis, 5th ed. Philadephia: F.A. Davis 2009. Objectives Classify the hemolytic anemias into intracorpuscular and extracorpuscular Identify the red cell membrane abnormalities associated with hereditary spherocytosis and hereditary elliptocytosis Discuss the clinical and laboratory findings hemolytic anemia caused by hereditary defects of red cell membrane List the enzymatic defects in RBC and the clinical and laboratory findings for each 2 1  11/13/2023 Hemolytic Anemia (HA) HA: a heterogeneous group of normocytic normochromic anemia, with premature destruction of red cells (hemolysis), or shortened red cell life span BM can increase its output 6-8-fold to compensate for anemia, which corresponds to RBC life span of 15-20 days 3 Classification of Hemolytic Anemia Intracorpuscular defects Hereditary defects Defects in red cell membrane Enzyme defects Hemoglobinopathies Thalassemia syndrome Acquired defects Paroxysmal nocturnal hemoglobinuria (PNH) 4 2  11/13/2023 Classification of Hemolytic Anemia Extracorpuscular defects Immune hemolytic anemia Infections Exposure to chemicals and toxins Exposure to physical agents Microangiopathic and macroangiopathic hemolytic anemias Splenic sequestration (hypersplenism) General systemic disorders (in which hemolysis is not the dominant feature of the anemia) 5 Diagnosis of HA: Establishing the Presence of Hemolysis Tests reflecting increased red cell Destruction Serum un-conjugated (indirect) bilirubin Extravascular Hemoglobinemia Intravascular Hemoglobinuria (dark urine) Hemosiderinuria (iron storage protein in a spun deposit of urine) Methemalbumin in the blood (Schumm’s test) Methemoglobinemia Serum Hemopexin Serum Haptoglobin (!) Urine urobilinogen & fecal stercobilinogen are increased 6 3  11/13/2023 Degradation of Hb After Intra- & Extra-vascular Hemolysis When present in large quantities, methemalbumin & Hemopexin-heme complex imparts a brownish color to plasma Figure 9-1 Diagrammatic representation of the degradation of hemoglobin after intravascular or extravascular destruction of red cells. Fe = iron; Hb = hemoglobin; RBC = red blood cell; R.E. = 7 reticuloendothelial cell. Progressive urine samples in acute intravascular hemolysis showing Hemoglobinuria of decreasing severity 8 4  11/13/2023 Prussian blue-positive deposits of Hemosiderin in a urine spun deposit (Perl’s stain) 9 Tests Reflecting Increased Red Cell Production Reticulocyte count Reticulocyte production index (RPI): corrects the Hct to normal value of 45% & takes into account the maturation time of Retic at a particular Hct (1.0, 1.5. 2.0, 2.5 days for Hct of 45, 35, 25 & 15%) RPI >2.5-3.0 is indicative of HA BM erythroid hyperplasia, M:E ratio from 3-4:1 is reduced to 1:1 or even reversed 10 5  11/13/2023 Special Tests: Osmotic Fragility Red Survival Studies Figure 9-2 Diagnostic approach to hemolytic anemias. 11 Box 9–1 Predominant Red Cell Morphology Commonly Associated with Nonimmune Hemolytic Disorders Spherocytes Elliptocytes Bizarre Poikilocytes Stomatocytes Hereditary spherocytosis Hereditary Red cell fragmentation Hereditary elliptocytosis syndrome stomatocytosis Acute oxidant injury (HMP (microangiopathic and and related shunt defects during Thalassemias macroangiopathic disorders hemolytic crisis, oxidant Iron deficiency hemolytic anemias) drugs and chemicals) Stomatocytic Megaloblastic Hereditary elliptocytosis Clostridium welchii anemia elliptocytosis in septicemia neonates Severe burns, other red cell Hereditary thermal injuries pyropoikilocytosis Spider, bee, and snake venoms Severe hypophosphatemia ATP = adenosine triphosphate; HMP = hexose monophosphate 12 6  11/13/2023 Box 9–1 Predominant Red Cell Morphology Commonly Associated with Nonimmune Hemolytic Disorders Irreversibly Sickled Intraerythrocyti Prominent Basophilic Spiculated or Crenated Cells c Parasites Stippling Red Cells Sickle cell anemia Malaria Thalassemias Acute hepatic necrosis (spur cell anemia) Symptomatic sickle Babesiosis Unstable hemoglobins syndromes Uremia Bartonellosis Lead poisoning Infantile pyknocytosis Pyrimidine-5′- nucleotidase deficiency Abetalipoproteinemia McLeod blood group ATP = adenosine triphosphate; HMP = hexose monophosphate 13 Box 9–1 Predominant Red Cell Morphology Commonly Associated with Nonimmune Hemolytic Disorders Target Cells Nonspecific or Normal Morphology Hemoglobins S, C, D, and E Embden–Meyerhof pathway defects Thalassemias HMP shunt defects Adenosine deaminase hyperactivity with low red cell ATP Hereditary xerocytosis Unstable hemoglobins Paroxysmal nocturnal hemoglobinuria Dyserythropoietic anemias Copper toxicity (Wilson's disease) Cation permeability defects Erythropoietic porphyria Vitamin E deficiency Hypersplenism ATP = adenosine triphosphate; HMP = hexose monophosphate 14 7  11/13/2023 Red Cell Membrane Structure Red cell deformability, is determined by Biconcave disc shape of red cell  Excess SA:Volume ratio  cell volume is 90 μm3 while SA enclosing it is~ 140 μm3 Cytoplasmic viscosity, determined by MCHC Viscoelastic properties of the membrane, which depend on the integrity of membrane skeleton 15 Red Cell Membrane Skeleton Network Figure 9-3 Transmission electron micrographs of negatively stained red blood cell membrane skeletons. A. An area of spread skeleton network. B, C. The hexagonal lattice made up of spectrin tetramers (Sp4), hexamers (Sp6), or double tetramers (2Sp4). Cross-linking junctional complexes contain short F-actin filaments and protein 4.1. Globular ankyrin structures are bound to spectrin filaments about 80 nm from their distal ends. 16 8  11/13/2023 RBC Membrane Proteins 17 Table 9–1 Properties of Selected Red Cell Membrane Proteins Implicated in Hemolytic Anemia *Proteins were separated via SDS–PAGE and stained with Coomassie blue or periodic acid–Schiff reagent (PAS). †Molecular weight is calculated from the amino acid sequence and expressed as kilodaltons (kD). HS = hereditary spherocytosis; HE = hereditary elliptocytosis; HPP = hereditary pyropoikilocytosis; 18 SAO = Southeast Asian ovalocytosis. 9  11/13/2023 Hereditary Defects of the Red Cell Membrane Classification of RBC Membrane Defects Mutations affecting membrane are many, but the effect on Phenotype can be classified into: Hereditary spherocytosis (HS) Hereditary elliptocytosis (HE) & morphologically related disorders including Hereditary pyropoikilocytosis (HPP) & South East Asian (SEA) Hereditary stomatocytosis Hereditary xerocytosis Hereditary acanthocytosis 20 10  11/13/2023 Classification of RBC Membrane Defects Type of red cell morphological changes (poikilocyte) depends on Vertical interactions like defects in spectrin-ankyrin-band 3 associations & spectrin-inner layer of PL bilayer  spherocytes Horizontal interactions like defects in spectrin dimer self-association & spectrin-actin-protein 4.1 complex formation  other poikilocytes 21 Defects in Red Cell Membrane in HS, HE & HPP Figure 9-5 Diagrammatic illustration of the vertical and horizontal interactions between the red cell membrane components (top). The bottom section illustrates the pathophysiology of the red cell lesion in hereditary spherocytosis (HS), hereditary elliptocytosis (HE), and hereditary pyropoikilocytosis (HPP). A defect in a vertical interaction resulting in spherocytes and HS is illustrated at the bottom left. A defect in a horizontal interaction resulting in elliptocytes and poikilocytes (HE and HPP) is illustrated at the 22 bottom right. 11  11/13/2023 Hereditary Spherocytosis (HS) Inheritance: Autosomal Dominant Most Common Defects of RBC Membrane proteins in HS Protein deficiencies Spectrin Ankyrin & spectrin Band 3 Protein 4.2 Pathophysiology: Loss of SA which results in decreased SA:Vol ratio  spherocytes Increased permeability of the membrane to Sodium 23 Figure 9-6 Photomicrograph of peripheral blood smear from a patient with hereditary spherocytosis (HS). Note the microspherocytes (small condensed spherocytes with no central pallor), indicated by the black arrow and the pincered (mushroom-shaped) cell, indicated by the white arrow. 24 12  11/13/2023 Figure 9-7 Schematic Splenic representation of postulated mechanisms of “conditioning” Conditioning and destruction of HS red cells in the spleen. of RBCs in HS 25 Extravascular Hemolysis Schematic of splenic sinus. An erythrocyte is in the process of squeezing from the cord into the sinus lumen. Note the degree of deformability required for the RBCs to pass through the wall of the sinus. 26 13  11/13/2023 Hereditary Spherocytosis (HS) spherical shape, which are less deformable than normal and are therefore trapped in the splenic cords, where they are phagocytosed by macrophages. Membrane loss and red cell trapping occur in the splenic microcirculation. 27 Clinical Manifestation of HS Classic triad of jaundice, anemia, and enlarged spleen (splenomegaly) A minority of patients (10%) have severe HA  require blood transfusion Aplastic crisis leads to more pronounced anemia Hemolytic crisis with acute infections  increased hemolysis  gallstones due to increased bilirubin Leg ulcers due to prolonged hemolysis 28 14  11/13/2023 Figure 9-8 Laboratory diagnosis of HS using a Technicon H1 laser scattering automated blood counter. A. The histogram indicates a subpopulation of microcytes with a low mean cell volume (MCV) in a patient with HS. B. The histogram depicts a subpopulation of dehydrated HS red cells with a high mean cell hemoglobin concentration (MCHC). 29 Lab Findings Evidence of hemolytic process> extravascular hemolysis Hyperbilirubinemia Reduced Haptoglobin levels RPI>2.5 Red cell indices (heterozygote) Hb 12-13 g/dl MCV usually N, but can be L or H MCH parallels MCV MCHC increased in ~50% of cases(>37g/dl) 30 15  11/13/2023 Lab Findings Red cell morphology of peripheral smear Microspherocytes, but their number varies considerably There may be varying degrees of polychromasia, poikilocytosis & anisocytosis Presence of acanthocytes in patients with B-spectrin defects Special tests Osmotic fragility test Autohemolysis studies (in HS  corrected with glucose) Red cell membrane studies 31 Hereditary Spherocytosis (HS) Increased Osmotic Fragility: – RBCs are placed in a series of hypotonic salt; swell; equilibrium leaks Hb & burst. – Spherocytes tolerate less than normal because of decreased surface area to volume ratio  lyse at higher concentration of salt than normal. – If mild, 25% have normal Osmotic fragility. 32 16  11/13/2023 Osmotic Fragility Test in HS HS before splenectomy HS after splenectomy Very fragile cells 33 Figure 9-9 Osmotic fragility curves of fresh blood (top) and incubated blood (bottom) obtained from a patient with HS. The normal range is shown by blue areas. Note the increased fragility of the HS red cells to osmotic lysis. 34 17  11/13/2023 Treatment for HS Splenectomy After splenectomy, spherocytes persist, but conditioned microspherocytes are no longer seen and their life span is N or near N Splenectomy is preferably delayed after the age of 6 years because of the risk of infections 35 Hereditary Elliptocytosis (HE) A group of disorders characterized by the presence of Elliptocytes in PB, most persons asymptomatic due to normal erythrocyte life span Inheritance: usually Autosomal dominant Common HE including: Hereditary pyropoikilocytosis (HPP): Misshapen budding (severe hemolysis) Spherocytic HE Southeast Asian ovalocytosis (SAO) 36 18  11/13/2023 HE & HPP HPP Relatively rare Moderate to severe hemolysis Smear shows microspherocyes, micropoikilocytosis, fragments & few if any elliptocytes Patients are usually heterozygotes  defective spectrin dimer self-association; partial spectrin deficiency 37 HE & HPP Spherocytic HE A hybrid of HE & HS, with clinical course resembling HS SAO or stomatocytic HE Common Melanesian & SAE, usually asymptomatic  protective against malaria Occurs also in South Africa, usually associated with mild hemolysis 38 19  11/13/2023 Defects in Red Cell Membrane in HS, HE & HPP Figure 9-5 Diagrammatic illustration of the vertical and horizontal interactions between the red cell membrane components (top). The bottom section illustrates the pathophysiology of the red cell lesion in hereditary spherocytosis (HS), hereditary elliptocytosis (HE), and hereditary pyropoikilocytosis (HPP). A defect in a vertical interaction resulting in spherocytes and HS is illustrated at the bottom left. A defect in a horizontal interaction resulting in elliptocytes and poikilocytes (HE and HPP) is illustrated at the 39 bottom right. Lab Findings of HE & HPP In mild cases: slight reticulocytosis, Decreased haptoglobin In severe cases: features of extravascular hemolysis Morphology of peripheral smear Mild HE: usually >30% of RBCs are uniform elliptocytes (in some cases >75%) HPP: Cells show increased thermal sensitivity, Misshapen budding Spheocytic HE: less prominent elliptocytosis, with spherocytes & microspherocytosis In SAO or stomatocytic HE: elliptocytes are round & oval with transverse bar. Cells are quite large 40 20  11/13/2023 HE & HPP: Lab Features Elliptocytosis: Poikilocytosis: Hereditary elliptocytosis. Hereditary pyropoikilocytosis. Small lymphocyte in field Small lymphocyte in field 41 Figure 9-10 Photomicrograph of peripheral blood smear from a patient with mild hereditary elliptocytosis (HE). Note the high percentage of elliptocytes. 42 21  11/13/2023 Figure 9-11 Photomicrograph of peripheral blood smear from a patient with hereditary pyropoikilocytosis (HPP). Note the bizarre micropoikilocytosis, red cell budding, and very few elliptocytes. 43 Figure 9-12 Photomicrograph of peripheral blood smear from a patient with Southeast Asian ovalocytosis (SAO). Note the characteristic spoon- shaped oval cells with a band across the central area. 44 22  11/13/2023 Figure 9-13 Photomicrograph of peripheral blood smear from a patient with mild HE and poikilocytosis of infancy. Note the poikilocytosis and fragmentation. 45 Lab Findings of HE & HPP Red cell indices MCV is N or slightly elevated MCH & MCHC, usually N In infants with HE & HPP: MCV is decreased; MCHC is N or slightly elevated In HPP: MCV is decreased, MCHC is usually elevated Osmotic fragility & Autohemolysis In HE: both are normal, rarely some patients may have increased A.H. corrected with Glucose HPP: OF is increased, A.H is increased/not corrected with glucose 46 23  11/13/2023 Hereditary Stomatocytosis (Hydrocytosis) & Hereditary Xerocytosis Membrane defect due to abnormal permeability cations to both sodium and potassium; causes erythrocyte swelling Inheritance: HSt: AD, or AR in some patients with severe hemolysis Hxe: AD Etiology: In Hst: defect in Na+ permeability, Na+ accumulate inside cells> hydrocytes In Hxe: defect in K+ permeability, loss of K+ dehydration (Xerocytosis) 47 Hereditary Stomatocytosis (Hydrocytosis) & Hereditary Xerocytosis Figure 9-15 Photomicrograph of peripheral blood smear Figure 9-14 Photomicrograph of peripheral blood from a patient with hereditary xerocytosis. Note the smear from a patient with hereditary characteristic target cells and cells with hemoglobin stomatocytosis. Note the high percentage of red cells concentrated on one side of the cell. 48 with a central slit of pallor. 24  11/13/2023 Lab Findings in Hst & HXe Morphology of PB smear Hst: stomatcytosis with a tendency toward macrocytosis Hxe: target cells, small spiculated echinocytes, & cells with Hb concentrated on one side Red cell indices MCV is elevated in both Hst & Hxe MCHC: decreased in Hst & increased in Hxe Special lab tests Osmotic fragility increased in Hst & decreased in Hxe 49 Hereditary Acanthocytosis (Abetalipoproteinemia) Autosomal recessive; mild anemia associated with steatorrhea, neurological and retinal abnormalities; 50-100% of erythrocytes are acanthocytes Increased cholesterol: lecithin ratio in the membrane due to abnormal plasma lipid concentrations; absence of serum B- lipoprotein needed for lipid transport 50 25  11/13/2023 Hereditary Enzyme Deficiencies RBC Metabolic Pathways (Embden- Myerhof Glycolytic Pathway): Anaerobic Glycolysis Components of glycolytic pathway: – Main glycolytic pathway – Three ancillary pathways Specific enzymopathies: G6PD & PK Figure 10-1 Red cell metabolic pathways. The nucleated red cell depends almost 52 exclusively on the breakdown of glucose for energy requirements. 26  11/13/2023 Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD) Sex-linked enzyme defect; most common enzyme deficiency in the hexose monophosphate shunt G6PD gene locus: Xq28 There are >400 variants, but only ~1/4 of theses cause enzyme defects Reduced glutathione levels are not maintained because of decreased NADPH generation. Results in oxidation of hemoglobin to methemoglobin (Fe3+); denatures to form Heinz bodies 53 Table 10–1 Distribution of Some Common G6PD Variants Population Usually Patients with A(-) Enzyme Type Associated type G-6-PD Gd B (normal variant) All deficiency are Gd Med (also known Whites least likely to as Gd B–) (Mediterranean area) have spontaneous Gd A+ (normal Blacks (~ 16% of hemolytic variant) African Americans) episodes Gd A– Africans Gd Canton Asians 54 27  11/13/2023 Pathogenesis G6PD Activity is highest in young RBCs and decreases with cell aging Under normal conditions, shortened red cell life span is compensated by increased erythropoiesis  increased Retics Oxidative stress mild to severe hemolysis Usually, not anemic until oxidatively challenged (primaquine, sulfa drugs); then severe hemolytic anemia with reticulocytosis Oxidants more than 50 drugs Examples: Nalidixic acid, chloramphenicol, sulafanilamide, primaquine (anti-malarial drug) 55 Favism Severe hemolysis after ingestion of fava beans or even inhaling the plant’s pollen Encountered mostly with G6PD- Mediter or Canton Figure 10-5 Fava beans. 56 28  11/13/2023 Clinical Findings Majority of patients are asymptomatic G6PD activity ~20% is sufficient for normal cell function 2-3 days after oxidant intake  RBC count decrease  anemia (normochromic normocytic) Hgb-uria & jaundice Bite cells Hemolytic disease of newborn  is rare with “Gd A-” but more common with “Gd Med” type Blood transfusion may be occasionally required with Gd Med type57 Figure 10-3 Heinz bodies, using Figure 10-4 Peripheral blood smear from a peripheral blood from a patient with patient with a G6PD deficiency. G6PD deficiency, stained with the Note the small, condensed “bite” or supravital stain, crystal violet. “helmet” cells. 58 29  11/13/2023 Table 10–3 Comparison of Clinical Features of Gd A– and Gd Med (Gd B–) Clinical Feature Gd A– Gd Med Cells affected by defect Aging erythrocytes All erythrocytes Hemolysis with drugs Unusual Common Hemolysis with infection Common Common Favism No Occasionally Degree of hemolysis Moderate Severe Transfusions required No Occasionally Chronic hemolysis No No Hemolytic disease Rare Occasionally 59 Lab Testing General: low Hct, Hgb-uria Heinz bodies, seen with supravital stain (may be seen with some unstable Hbs but not with PK deficiency) Elevated serum bilirubin Low or absent Haptoglobin Screening for G6PD using MetHb reductase test Screening  Fluorescent spot test Quantitative G6PD assay (should be done after the hemolytic crisis) 60 30  11/13/2023 RBCs with precipitates of denatured globin (Heinz bodies) revealed by supravital staining. As the splenic macrophages pluck out these inclusions, "bite cells“ (or helmet cells) like the one in this smear are produced Heinz bodies 61 Pyruvate Kinase (PK) Deficiency Inheritance: Autosomal recessive; most common enzyme deficiency in Embden-Meyerhof pathway Lack of ATP causes impairment of the cation pump that controls intracellular sodium and potassium levels. Decreased erythrocyte deformability reduces their life span. Severe hemolytic anemia with reticulocytosis and echinocytes Severity depend on properties of mutant enzyme Hemolytic anemia is more prominent during infection or other stresses ~3-fold increase in 2,3DPG level  decrease Hb affinity for O2 shift to right The second most common RBC enzyme deficiency, & together with G6PD constitute the most cases of HNSHA (Hereditary nonspherocytic hemolytic anemia) arising from RBC enzyme deficiency 62 31  11/13/2023 Lab Testing for PK Blood film: normochromic Moderate increase in serum normocytic anemia unconjugated bilirubin Poiklo- aniso-cytosis & NRBCs Haptoglobin is decreased or absent Low Hct & Hb Quantitative PK assay (red cells must be free from WBCs) Varying degree of Retic Screening tests include: osmotic Polycythemia may occur fragility  near normal Coomb’s test negative 63 Methemoglobin Reductase Deficiency Fe++ Fe+++ (ox) MetHb Reductase Inheritance: AR MetHb Reductase def.  MetHbemia (cyanosis) Some patients develop compensatory mild polycythemia MetHbemia may be caused by HbM disease (α58His_>Tyr) (or β chain) and acuter reaction to some drugs and toxins Differential diagnosis: by quantitative enzyme assay and Hb electrophoresis (identify abnormal Hbs) 64 32  11/13/2023 Assessment Questions Assessment-Q1 Which of the following characteristics are common to hereditary spherocytosis, hereditary elliptocytosis, hereditary stomatocytosis, and paroxysmal nocturnal hemoglobinuria? L1 A. autosomal dominant inheritance B. red cell membrane defects C. positive direct antiglobulin test D. measured platelet count 66 33  11/13/2023 Assessment-Q1 Which of the following characteristics are common to hereditary spherocytosis, hereditary elliptocytosis, hereditary stomatocytosis, and paroxysmal nocturnal hemoglobinuria? L1 A. autosomal dominant inheritance B. red cell membrane defects C. positive direct antiglobulin test D. measured platelet count 67 Assessment-Q2 Patients with A(-) type G-6-PD deficiency are least likely to have hemolytic episodes in which of the following situations? L1 A. following the administration of oxidizing drugs B. following the ingestion of fava beans C. during infections D. spontaneously 68 34  11/13/2023 Assessment-Q2 Patients with A(-) type G-6-PD deficiency are least likely to have hemolytic episodes in which of the following situations? L1 A. following the administration of oxidizing drugs B. following the ingestion of fava beans C. during infections D. spontaneously 69 Assessment-Q3 A patient has a congenital non spherocytic hemolytic anemia. After exposure to anti-malarial drugs the patient experiences a severe hemolytic episode. This episode is characterized by red cell inclusions caused by hemoglobin denaturation. Which of the following conditions is most consistent with these findings? L2 A. G-6-PD deficiency B. thalassemia major C. pyruvate kinase deficiency D. paroxysmal nocturnal hemoglobinuria 70 35  11/13/2023 Assessment-Q3 A patient has a congenital non spherocytic hemolytic anemia. After exposure to anti-malarial drugs the patient experiences a severe hemolytic episode. This episode is characterized by red cell inclusions caused by hemoglobin denaturation. Which of the following conditions is most consistent with these findings? L2 A. G-6-PD deficiency B. thalassemia major C. pyruvate kinase deficiency D. paroxysmal nocturnal hemoglobinuria 71 Assessment-Q4 Hereditary pyropoikilocytosis (HP) is a red cell membrane defect characterized by: A. Increased pencil-shaped cells B. Increased oval macrocytes C. Misshapen budding D. Bite cells 72 36  11/13/2023 Assessment-Q4 Hereditary pyropoikilocytosis (HP) is a red cell membrane defect characterized by: A. Increased pencil-shaped cells B. Increased oval macrocytes C. Misshapen budding D. Bite cells 73 Assessment-Q5 A 32-year-old African-American traveling to Africa on business had been healthy until he began taking primaquine for prevention of malaria. He went to his physician because he felt faint and his urine was black. His CBC results are as follows: WBC 6.5 X 109/L (6.5 X 103/µL); RBC 1.67 X 1012/L (1.67 x 106/µL|_); hemoglobin level 50 g/L (5.0 g/dL); hematocrit 0.15 L/L (15%); MCV 89.8 fL; MCHC 33.3 g/dL; platelet count 175 x 109/L (175,000/|µL); reticulocyte25.0%. The most likely cause of this haemolytic episode is A. G6PD deficiency B. Hereditary spherocytosis C. Sickle cell disease D. Pyruvate kinase deficiency 74 37  11/13/2023 Assessment-Q5 The defect in this disorder is caused by an L3 A. Amino acid substitution B. Intrinsic red blood cell membrane defect C. Enzyme deficiency in the hexose monophosphate shunt D. Enzyme deficiency in the Embden-Meyerhof pathway 75 Assessment-Q5 A 32-year-old African-American traveling to Africa on business had been healthy until he began taking primaquine for prevention of malaria. He went to his physician because he felt faint and his urine was black. His CBC results are as follows: WBC 6.5 X 109/L (6.5 X 103/µL); RBC 1.67 X 1012/L (1.67 x 106/µL|_); hemoglobin level 50 g/L (5.0 g/dL); hematocrit 0.15 L/L (15%); MCV 89.8 fL; MCHC 33.3 g/dL; platelet count 175 x 109/L (175,000/|µL); reticulocyte25.0%. The most likely cause of this haemolytic episode is A. G6PD deficiency B. Hereditary spherocytosis C. Sickle cell disease D. Pyruvate kinase deficiency 76 38  11/13/2023 Assessment-Q5 The defect in this disorder is caused by an L3 A. Amino acid substitution B. Intrinsic red blood cell membrane defect C. Enzyme deficiency in the hexose monophosphate shunt D. Enzyme deficiency in the Embden-Meyerhof pathway 77 End 78 39