Haemolytic Anaemia - Strictly According to Robbins Pathology

Robbins & Kumar Basic Pathology (Robbins Pathology), 10th ed., ISBN 9780323790185

Definition and Overview

• Marrow erythroid hyperplasia
• Peripheral blood reticulocytosis (hallmarks of haemolytic anaemia)
• In severe cases: extramedullary haematopoiesis in liver, spleen, and lymph nodes

Classification

1. By Origin of Defect

2. By Site of Haemolysis (Clinically more useful)

Extravascular Haemolysis

• Hyperbilirubinaemia and jaundice (from Hb degradation in macrophages)
• Splenomegaly (work hyperplasia of phagocytes)
• Cholelithiasis with pigment (bilirubin-rich) gallstones if long-standing
• Low serum haptoglobin (macrophages regurgitate enough Hb to deplete it)
• No iron deficiency (iron recycling by phagocytes is efficient)

Intravascular Haemolysis

• Haemoglobinaemia - free Hb in plasma
• Haemoglobinuria - Hb passes into urine (Hb molecule is small enough)
• Haemosiderinuria - iron accumulation in renal tubular cells shed into urine
• Iron deficiency - iron is lost via urine rather than recycled
• Low serum haptoglobin (also seen in extravascular)

Types of Haemolytic Anaemia

1. Hereditary Spherocytosis

• Spectrin (major protein) - long, flexible heterodimer
• Actin filaments
• Ankyrin and band 4.1 - linker proteins
• Connected to intrinsic membrane proteins band 3 and glycophorin

• Peripheral smear: spherocytes are dark red and lack central pallor
• Compensatory marrow erythroid hyperplasia + reticulocytosis
• Splenomegaly (most prominent of all haemolytic anaemias) - splenic weight 500-1000 g (normal 150-200 g)
• Marked congestion of splenic cords, increased macrophages
• Cholelithiasis in 40-50% of patients

2. Sickle Cell Anaemia

• HbS differs from HbA: valine instead of glutamate at β-globin position 6
• On deoxygenation, HbS molecules undergo conformational change → polymers form via intermolecular contacts involving the abnormal valine → red cells assume elongated crescentic (sickle) shape
• Sickling is initially reversible on reoxygenation; with repeated episodes → membrane damage (calcium influx, K⁺ and water loss) → irreversibly sickled cells → haemolysis

1. Intracellular levels of non-HbS Hb - HbA retards HbS polymerization greatly → HbS heterozygotes (sickle cell trait) have little sickling in vivo. HbF also retards polymerization → newborns asymptomatic until HbF falls (~5-6 months). HbC (lysine instead of glutamate) interacts with HbS only moderately → compound heterozygotes have milder disease
2. Intracellular Hb concentration - high MCHC favours polymerization; dehydration worsens sickling
3. Length of time in deoxygenated state - slow blood flow prolongs deoxygenation

• Peripheral smear: sickle-shaped red cells, target cells, nucleated red cells
• Vaso-occlusive crises - hallmark; microinfarcts in bones, spleen, liver, brain, lungs, penis
• Spleen: initially enlarged by red pulp congestion with sickled cells; progressive splenic infarction leads to autosplenectomy (fibrotic, shrunken spleen by adulthood)
• Severe splenomegaly can occur in compound heterozygotes (HbSC)
• Bone marrow hyperplasia → cortical bone thinning, "crew cut" appearance on skull X-ray
• Increased risk of aplastic crisis (Parvovirus B19), sequestration crisis, infections by encapsulated bacteria (functional asplenia)

1. Increasing HbF levels
2. Anti-inflammatory effect (inhibits WBC production)
3. Increases red cell size, lowering intracellular Hb concentration
4. Metabolizes to NO (vasodilator, inhibits platelet aggregation)

3. Thalassemia

β-Thalassemia

• Point mutations impair transcription, splicing, or translation of β-globin mRNA
• Excess α-globin chains form insoluble precipitates → damage red cell membranes → ineffective erythropoiesis (destruction of erythroid precursors in marrow) + haemolysis
• Both extravascular haemolysis and ineffective erythropoiesis contribute to anaemia

• Marked microcytosis, hypochromia, poikilocytosis, anisocytosis, nucleated red cells (normoblasts)
• Target cells (increased surface area-to-volume ratio)
• Striking erythroid hyperplasia filling intramedullary space → cortical bone thinning, impaired growth, skeletal deformities
• Extramedullary haematopoiesis → prominent splenomegaly, hepatomegaly, lymphadenopathy
• Growth retardation and cachexia
• Severe haemosiderosis from iron overload (transfusions + increased gut iron absorption due to suppressed hepcidin from expanded erythropoiesis)

• β-Thalassemia minor/trait: asymptomatic, normal life expectancy; mild microcytic hypochromic anaemia
• β-Thalassemia major: manifests postnatally as HbF diminishes; growth retardation from infancy; survival into 2nd-3rd decade with transfusions, but iron overload develops; chelation therapy (deferoxamine) + bone marrow transplant can be curative

α-Thalassemia

• Caused by deletion of α-globin genes (usually entire genes deleted)
• Severity depends on number of genes deleted (0-4):
  • 1 gene deleted: silent carrier state
  • 2 genes deleted: α-thalassemia trait - mild microcytic anaemia
  • 3 genes deleted: HbH disease - excess β-chains form β₄ tetramers (HbH); relatively stable but high O₂ affinity (poor O₂ delivery)
  • 4 genes deleted: Hydrops fetalis - lethal in utero; excess γ-chains form γ₄ (Hb Bart); near-zero O₂ delivery capacity

4. Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency

• Oxidant stress (from drugs, infections, foods) overwhelms deficient GSH
• Oxidants attack globin chains → oxidized haemoglobin denatures → precipitates as Heinz bodies (intracellular inclusions)
• Heinz bodies damage the red cell membrane → intravascular haemolysis
• Cells with less damage lose deformability; splenic macrophages "pluck out" Heinz bodies → bite cells (Fig. 10.6) → trapped and destroyed in spleen

• Antimalarials (primaquine), sulfonamides, nitrofurantoin, phenacetin, high-dose aspirin, vitamin K derivatives
• Fava beans (favism)
• Infections (most common trigger - phagocytes generate oxidants as host response)

• Haemolysis 2-3 days after drug exposure; variable severity
• Males uniformly affected (X-linked)
• Heterozygous females: two RBC populations due to lyonization; most unaffected unless "unfavorable lyonization" (large proportion of deficient cells)
• G6PD A- variant (Africa): only older red cells lysed (modest enzyme decrease); haemolysis self-limited as marrow replaces with new cells with adequate G6PD
• G6PD Mediterranean (Middle East): more marked deficiency; more severe haemolysis

5. Paroxysmal Nocturnal Haemoglobinuria (PNH)

• Classic (but uncommon) presentation: nocturnal haemolysis (sleep-related CO₂ retention → decreased pH → enhanced complement fixation)
• Most present with chronic anaemia and iron deficiency from chronic intravascular haemolysis
• Association with aplastic anaemia (may precede or follow PNH)
• Most feared complication: thrombosis in abdominal vessels (portal vein, hepatic vein) - related to excessive complement activity

• Does NOT affect early complement fixation → C3b continues to deposit → continuing extravascular haemolysis
• Blocks C5b-C9 → risk of Neisseria (meningococcal) infections → all patients must be vaccinated against N. meningococcus

6. Immunohemolytic Anaemia

Warm Antibody Type

• IgG (rarely IgA) antibodies active at 37°C

• 60% idiopathic; 25% in immunologic disorders (SLE) or drug-induced

• Mechanism: IgG-coated cells phagocytosed in spleen; also "nibbling" by macrophages removes membrane → spherocytes → rapid splenic destruction (same as hereditary spherocytosis)
• Drug mechanisms:
  • α-methyldopa: induces autoantibodies against Rh blood group antigens
  • Penicillin: binds covalently to red cell membrane proteins → neoantigens → antibody response
  • Some drugs form immune complexes that deposit on red cells → fix complement or act as opsonins

Cold Antibody Type

• Low-affinity IgM antibodies binding at temperatures <30°C (e.g., distal extremities in cold)
• Transient forms: Mycoplasma pneumonia, infectious mononucleosis (mild, clinically unimportant)
• Chronic forms: B-cell neoplasms or idiopathic
• Pathogenesis: IgM initiates complement fixation; later steps inefficient at <37°C → cells coated with C3b and C3d but not lysed. In warm areas, IgM released but C3b/C3d remain → phagocytosis by macrophages (mainly spleen and liver) → mostly extravascular haemolysis
• IgM pentavalency → crosslinks red cells → agglutination → sludging in capillaries → Raynaud phenomenon

7. Mechanical Haemolysis

1. Traumatic (macroangiopathic) haemolysis:
   • Dysfunctional cardiac valve prostheses - turbulence creates "blender effect"
   • Repeated physical pounding (marathon racing, karate, bongo drumming)
2. Microangiopathic haemolytic anaemia (MAHA):
   • Small vessels partially obstructed by fibrin strands, platelet thrombi, or other lesions → passing red cells are sheared into schistocytes (helmet cells, triangular cells)
   • Causes: DIC (most common - fibrin deposition), severe hypertension, thrombotic thrombocytopenic purpura (TTP), haemolytic-uraemic syndrome (HUS)

8. Malaria

• Haemolysis caused by Plasmodium parasites invading and destroying red cells
• P. falciparum is the most severe form; protective pressure explains why HbS, G6PD deficiency, and thalassemia mutations are prevalent in malaria-endemic areas
• Haemolysis is both intravascular (rupture of parasitized cells) and extravascular (phagocytosis of parasitized cells)

Summary Table