RBC Disorders 1 &2

Question 1

Hereditary spherocytosis

Answer 1

inherited intrinsic defect causing extravascular hemolysis

Question 2

Hereditary Spherocytosis etiology

Answer 2

autosomal dominant mutations in genes coding for membrane proteins of RBC- most commonly ankyrin

Question 3

Hereditary Spherocytosis clinical features

Answer 3

Anemia
Splenomegaly
Unconjugated hyperbilirubinemia
Increased LDH

Question 4

Pathogenesis of hereditary spherocytosis

Answer 4

Reduced RBC membrane stability→ Loss of small fragments during normal shearing stresses in the blood circulation→ RBCs become increasingly more spherical→unable to traverse the splenic sinusoids→phagocytosis and destruction by splenic macrophages (spleen usually enlarged)

Cells also become dehydrated in spleen + loss of surface area → MCHC increases

Question 5

Hematological Findings of HS

Answer 5

Hematological Findings

1. Normocytic normochromic RBCs
2. Spherocytes (lack of central pallor)
3. Polychromatophilic cells± nucleated RBCs
4. If splenectomy-HowellJollybodies
5. MCHC high

Osmotic Fragility Test:
• To confirm the presence of spherocytes
• Spherocytic RBCs lyse prematurely (compared to normal RBCs), when exposed
to increasingly hypotonic salt solutions→less space for expansion

Question 6

Micro/Macroangiopathic Hemolytic Anemias

Answer 6

1. Macroangiopathic hemolytic anemia- (large vessel)- hemolysis stems from shear forces produced by turbulent blood flow and pressure gradients across damaged/prosthetic valves
2. Microangiopathic hemolytic anemia (MAHA)- micro vascular lesions ; shear stresses that mechanically injure passing red cells.

• Most commonly seen with disseminated intravascular coagulation (DIC),

Peripheral blood- schistocytes/ fragmented RBCs

Question 7

Paroxysmal Nocturnal Hemoglobinuria

Answer 7

• Acquired genetic mutation in PIGA gene on Hematopoietic stem cell →
• No GPI anchored proteins formed normally →
• No structural support for complement regulatory
proteins (c8 binding protein, DAF Cd55, MIRL CD59)
• Complement mediated intravascular damage to RBCs

Decrease in blood ph when asleep increases the activity of complement

• episodic
• pancytopenia

Question 8

Triad seen in Paroxysmal Nocturnal Hemoglobinuria

Answer 8

PANCYTOPENIA + THROMBOSIS + HEMOLYTIC ANEMIA

Question 9

Paroxysmal Nocturnal Hemoglobinuria la investigations

Answer 9

Coomb’s test
NEGATIVE (differentiate from autoimmune hemolytic anemia- AIHA- antibody mediated destruction of RBCs)

Flow cytometry
RBCs negative for CD 55 and CD 59

Early morning urine samples- dark

• Indirect hyperbilirubinemia; Low haptoglobin; High LDH
• Low serum iron

Question 10

G6PD Deficiency

Answer 10

• Glucose 6 phosphate dehydrogenase(G6PD) deficiency
• X linked recessive inheritance
• Triggers of oxidative damage like infections,
drugs (antimalarials like primaquine, or sulfonamides) or ingestion of fava beans → no protection from free radicals

Heinz bodies -> Intravascular hemolysis
Spherocytes -> less deformable-> extravascular hemolysis
Bite cells

Question 11

What happens if we do a G6PD assay immediately after an episode

Answer 11

• cells with no G6PD would have been lysed.
• Only younger cells with enzyme activity will remain.
• false negative test
• Hence, we wait at least 3 months after the hemolytic episode.

Question 12

Clinical features and hematological findings of G6PD deficiency

Answer 12

Hematological Findings

1. Normocytic normochromic RBCs
2. Bitecellsand Spherocytes
3. Heinzbodieson supravital stain
4. Polychromatophiliccells ± nucleated RBCs
5. During hemolytic episode- other findings of hemolysis

Clinical features

• x linked
• acute hemolysis
• begins 2-3 days following exposure
• Only older red cells are at risk for lysis → hemolysis ceases when only younger G6PD-replete red cells remain (even if exposure to the trigger, e.g., an offending drug, continues)→episode is self-limited
• Recovery phase→ reticulocytosis

Question 13

Hemoglobinopathies

Answer 13

• Quantitative hemoglobinopathy – deficient production of α or β globin chains –
Thalassemia (α and β thalassemias)
• Qualitative hemoglobinopathy – change in structure of globin chain – Sickle
cell disease (defect in β globin chain)

Question 14

Sickle cell anemia

Answer 14

• Missense point mutation in the β-globin gene that leads to the replacement of a charged glutamate residue with a hydrophobic valine residue at the 6th position in the amino acid chain
• Mutant beta joins normal alpha to make mutant HbS→less soluble→polymerises in deoxygenated states, in acidosis or high altitude
• Red cell cytosol changes from a freely flowing liquid into a viscous gel (concentration dependent – more HbS→ more polymerization)
• With continued deoxygenation → HbS
molecules assemble into long needlelike
fibers→herniate through the membrane
skeleton and project from the cell

Question 15

if a cell has both HbS and HbC→sickling _________

if a cell has both HbS and HbF-> interferes with sickling hence infants do not become symptomatic before 6 months

Answer 15

if a cell has both HbS and HbC→sickling increases

if a cell has both HbS and HbF-> interferes with sickling hence infants do not become symptomatic before 6 months

Question 16

What does hydroxyurea do

Answer 16

increases the amount of HbF in RBCs→inhibits polymerization of HbS

Question 17

Alpha thalassemia and sickle cell

Answer 17

less alpha for mutated globin to bind to→decreased MCHC →sickling decreases

Question 18

Clinical features of sickle cell

Answer 18

• Moderately severe hemolytic anemia
• Early childhood- splenomegaly
• Bone marrow→compensatory erythroid hyperplasia
• Marked expansion of the marrow leads to bone resorption and secondary new bone formation→producing prominent cheekbones and changes in the skull that resemble a “crewcut” on radiographic studies
• Hyperbilirubinemia and formation of pigment gallstones

Autosplenectomy —> Howell jolly bodies

Chronic hypoxia

Question 19

Sequestration, aplastic and vaso occlusive pain crises

Answer 19

1. SEQUESTRATION CRISES
   • Occur in children with intact spleens
   • Massive entrapment of sickled red cells leads to rapid splenic enlargement, hypovolemia, and sometimes shock
2. APLASTIC CRISES - parvovirus B19 infecting RBC precursors
3. VASO- OCCLUSIVE/PAIN CRISES

• Episodes of hypoxic injury and infarction that cause severe pain in the affected region

Osteomyelitis especially due to Salmonella species

Question 20

Sickle cell anemia lab investigations

Answer 20

Question 21

Thalassemias

Answer 21

• Autosomal recessive
• decrease the synthesis of either α-globin or β-globin, leading to anemia, tissue hypoxia, and red cell hemolysis related to the imbalance in globin chain synthesis
• Splicing mutations and promotor region mutations→reduced globin from that allele → called β+ allele
• Chain terminator mutations→no globin from that allele→called βo allele

Question 22

β Thalassemia major/ Cooley’s anemia

Answer 22

Genotype : Homozygous (both alleles mutated)
βoβo
β+β+
β+βo

Severe anemia (3-6 g/dL) by 6-9 months Requires regular blood transfusions iron overload→hemochromatosis (liver, heart, pancreas)

Question 23

β Thalassemia intermedia

Answer 23

Variable genotype
Moderate to severe anemia
Doesn’t require transfusions regularly

Question 24

β Thalassemia minor/ trait

Answer 24

Heterozygous (only one allele mutated)
βoβ
β+β

Asymptomatic with mild or absent anemia
Red cell abnormalities seen in smear

Question 25

Thalassemia Pathogenesis

Answer 25

Beta globin chains very less

• Causes microcytic hypochromic cells
• Less globin and more membrane→ target cells

Alpha globin in excess
- Excess unpaired alpha globins form unstable tetramers
• Can precipitate in erythroid precursors; apoptosis leads to basophilic stippling
• Can precipitate in mature RBCs; tear drop cells and extravascular hemolysis—>
• Splenomegaly
• Compensatory erythropoiesis- crew cut appearance

Question 26

Beta thalassemia major vs Beta thalassemia minor

Answer 26

Question 27

Alpha thalassemias

Answer 27