Hereditary Spherocytosis and Elliptocytosis

Key Mechanism 1: Disrupted Membrane Skeleton Architecture

• The RBC membrane consists of a phospholipid bilayer anchored to an underlying cytoskeletal network composed of spectrin heterodimers, ankyrin, band 3, protein 4.2, and other linking proteins
• In HS, mutations in β-spectrin (most common), ankyrin, band 3, protein 4.2, or RhAG disrupt vertical linkages between the bilayer and cytoskeleton
• Ankyrin serves as the critical linker between band 3 (an anion exchanger and integral membrane protein) and spectrin (the primary horizontal support structure); loss of ankyrin function is the most frequent abnormality in HS
• In HE, mutations in α-spectrin or β-spectrin disrupt horizontal interactions within the spectrin lattice itself, creating abnormal RBC shape without necessarily compromising structural integrity
• Loss of normal protein interactions leads to membrane instability, progressive loss of membrane lipids, and deformability defects

Key Mechanism 2: Osmotic Fragility and Hemolysis

• Defective membrane skeleton proteins cause loss of deformability; spherocytes cannot deform appropriately in response to osmotic stress
• When RBCs transit through the splenic microcirculation, the spleen filters RBCs through narrow slits in the red pulp cords; normal RBCs deform substantially, but spherocytes and elliptocytes become mechanically trapped
• Splenic conditioning exacerbates the problem: repeated passage through the spleen causes progressive lipid loss from the membrane, making cells more rigid and more prone to sphering (in HS) or fracturing (in HE)
• Osmotic fragility test: In hypotonic solutions, normal RBCs can absorb water and swell, distributing water volume across a normal surface area; spherocytes, which already have a decreased surface area-to-volume ratio, cannot accommodate additional water and hemolyze at higher osmotic pressures
• RBCs undergo complement-mediated intravascular hemolysis and predominantly antibody-independent extravascular hemolysis via splenic macrophages recognizing abnormal RBC shape and membrane irregularities
• Chronic hemolysis leads to increased indirect hyperbilirubinemia, reticulocytosis, and iron overload with repeated transfusions

Key Mechanism 3: Molecular Heterogeneity in HS vs. HE

• HS mutations typically involve genes encoding vertical linkage proteins (ankyrin, band 3, RhAG, protein 4.2); vertical defects destabilize the entire membrane, promoting excessive sphering
• HE mutations typically involve spectrin genes; horizontal defects allow membrane skeleton to separate from the lipid bilayer but preserve some structural integrity, resulting in elliptical morphology rather than spherical
• α-Spectrin mutations account for approximately 50% of HE cases; β-spectrin mutations account for 25%; remaining cases involve protein 4.1 and other skeletal proteins
• Common HS variants:
• Spectrin-deficient HS: Reduced α-spectrin or β-spectrin levels (usually heterozygous); mildest form
• Ankyrin-deficient HS: Loss of ankyrin; severe form
• Band 3-deficient HS: Loss of band 3; severe form

Hereditary Spherocytosis

• Autosomal dominant inheritance in approximately 75% of cases; vertical protein gene mutations (ANK1, SLC4A1 [band 3], EPB42 [protein 4.2], RHAG)
• Autosomal recessive inheritance in approximately 25% of cases; typically requires homozygous or compound heterozygous mutations
• De novo mutations present in 5–10% of cases with negative family history
• Most common gene defects (in order of frequency):
• ANK1 (ankyrin, chromosome 8p11.2): ~50% of autosomal dominant cases
• SLC4A1 (band 3, chromosome 17q21): ~25% of cases
• SPTA1 (α-spectrin, chromosome 1q21): ~5% of cases
• SPTB (β-spectrin, chromosome 14q23): ~5% of cases
• EPB42 (protein 4.2, chromosome 15q15): ~5% of cases
• RHAG (RhAG, chromosome 6p21): <5% of cases

Hereditary Elliptocytosis

• Autosomal dominant inheritance in >95% of cases
• SPTA1 (α-spectrin, chromosome 1q21): ~50% of HE cases
• SPTB (β-spectrin, chromosome 14q23): ~25% of HE cases
• EPB41 (protein 4.1, chromosome 19p13.2): ~15% of HE cases
• Autosomal recessive HE (Southeast Asian ovalocytosis, SAO) associated with Band 3 mutations (Δ27 deletion); relatively benign with no hemolysis

Cardinal Symptoms

• Jaundice: Present in infancy or early childhood in moderate-to-severe HS; usually absent in mild HS or HE; results from unconjugated hyperbilirubinemia secondary to chronic extravascular hemolysis; often first sign
• Anemia: Variable severity depending on genetic defect; mild HS may present with Hgb 10–12 g/dL and minimal symptoms, while severe HS may present with Hgb 6–8 g/dL requiring transfusion; HE typically presents with mild anemia or no anemia
• Fatigue and dyspnea on exertion: Correlate with severity of anemia; more prominent in moderate-to-severe HS
• Splenomegaly: Present in 50–75% of HS patients; massive splenomegaly may develop in severe cases; results from extramedullary hematopoiesis (RBC production in spleen) and splenic macrophage proliferation; HE typically shows mild or absent splenomegaly
• Splenic crisis: Sudden worsening of hemolysis with severe anemia, jaundice, and abdominal pain; may be precipitated by infection (especially parvovirus B19), hypoxia, or dehydration; differs from aplastic crisis (see Complications)
• Cholelithiasis (gallstones): Occur in 50–60% of HS patients by age 40; secondary to chronic elevation of unconjugated bilirubin resulting in bilirubin gallstones; rare in HE due to lower hemolysis burden
• Leg ulcers: Rare but may develop in severe HS, analogous to those seen in chronic hemolytic anemias; related to chronic tissue hypoxia and high-output cardiac demands
• Growth retardation and developmental delay: May occur in severely affected children with high transfusion requirements

Physical Examination Findings

• Scleral icterus and jaundice: Visible in moderate-to-severe cases
• Splenomegaly: Usually moderate, but can be massive in severe disease
• Hepatomegaly: Less common than splenomegaly; present in some cases with significant hemolysis
• Pallor: Reflects degree of anemia
• Systolic murmur: High-output cardiac murmur (functional/flow murmur) secondary to anemia-induced increased cardiac output

Laboratory and Imaging Correlates

• Complete blood count:
• RBC morphology: Spherocytes on peripheral smear (HS) vs. elliptocytes or ovalocytes (HE)
• Mean corpuscular hemoglobin concentration (MCHC): Characteristically elevated in HS (distinguishes from other hemolytic anemias) because spherocytes have less surface area relative to volume, appearing more densely stained; MCHC is normal-to-low in HE
• Reticulocyte count: Elevated (typically 3–20%), reflecting compensatory erythropoiesis
• Hemoglobin level: Variable, ranging from normal to severe anemia
• Peripheral blood smear:
• HS: Numerous dense, dark-staining spherocytes (smaller, more condensed cells lacking central pallor); polychromasia (blue-tinged cells = reticulocytes); possible nucleated RBCs in severe cases
• HE: Rod-shaped, elliptical, or pencil-shaped RBCs; occasional fragmented RBCs or schistocytes; milder morphological changes than HS
• Osmotic fragility test (rarely used now but still a classic board exam topic):
• HS: Increased osmotic fragility; RBCs hemolyze at higher osmotic pressures (e.g., 0.36% saline) compared to normal RBCs (hemolyze at ~0.30% saline)
• HE: Normal osmotic fragility
• Mechanism: Spherocytes already have reduced surface area-to-volume ratio; cannot accommodate additional water
• Eosin-5-maleimide (EMA) flow cytometry (modern diagnostic test):
• EMA binds to band 3 and other RBC membrane proteins
• HS: Reduced or absent EMA binding due to band 3 deficiency or dysfunction
• HE: Normal EMA binding
• Sensitivity ~98%, specificity >99%; now gold standard for diagnosis
• Acidified glycerol lysis test:
• Measures resistance of RBCs to lysis in acidic glycerol solution
• HS: Increased osmotic fragility correlates with increased lysis
• Less commonly used than EMA flow cytometry
• Hemolysis markers:
• Elevated unconjugated (indirect) bilirubin: 1–3 mg/dL typical
• Elevated lactate dehydrogenase (LDH): Reflects RBC breakdown
• Elevated reticulocyte count: >3% (compared to normal <2%)
• Decreased haptoglobin: Consumed by binding free hemoglobin released from lysed RBCs
• Elevated urobilinogen in urine: Product of bilirubin metabolism
• Direct antiglobulin test (DAT/Coombs test): Negative in both HS and HE (distinguishes from autoimmune hemolytic anemia)
• Ultrasound abdomen:
• Documents splenomegaly and splenic size
• Identifies cholelithiasis (common in HS)
• May show hepatomegaly
• Abdominal imaging in crisis: Rules out alternative diagnoses; may show splenic infarction in severe hemolytic crisis

Histological Findings (Bone Marrow)

• Erythroid hyperplasia: Increased normoblastic (erythroid) precursors with normal maturation; M:E ratio reversed (E:M >1), reflecting compensatory RBC production
• Iron stores: Normal to depleted (if chronic transfusions or chronic blood loss)
• Fibrosis or necrosis: Absent unless complicated by infection (splenic infarction) or parvovirus-induced aplasia

Gross Pathology (Spleen)

• Splenomegaly: Weight typically 300–500 g (normal ~150 g); can exceed 1 kg in severe cases
• Dark red color: Congestion from RBC accumulation and macrophage activity
• Prominent germinal centers: Reactive lymphoid follicles
• Extramedullary hematopoiesis: May be microscopically evident

Microscopic Pathology (Splenic Red Pulp)

• Macrophage infiltration: Prominent macrophages within splenic cords; engulf abnormal RBCs
• Phagocytosed RBCs: RBC fragments within macrophages (demonstrating erythrophagocytosis)
• Congestion: Accumulation of RBCs within splenic sinuses

Laboratory Values

• Hemoglobin: 6–12 g/dL (depends on severity)
• MCV: Normal-to-low-normal
• MCHC: Elevated in HS (30–37 g/dL; normal 32–36); normal in HE
• Reticulocyte count: 3–20% (elevated)
• Bilirubin (unconjugated): 1–3 mg/dL
• LDH: >800 IU/L (elevated)
• Haptoglobin: <25 mg/dL (often <10 mg/dL; depleted)
• DAT (Coombs): Negative
• Osmotic fragility: Increased in HS; normal in HE

Diagnostic Criteria for HS

1. 1.Clinical evidence of hemolysis (jaundice, anemia, splenomegaly) ± family history
2. 2.Spherocytes on peripheral smear
3. 3.Elevated osmotic fragility OR positive EMA flow cytometry
4. 4.Negative DAT (excludes autoimmune hemolysis)
5. 5.Optional: Genetic testing for confirmation (ANK1, SLC4A1, SPTA1, SPTB, EPB42, RHAG mutations)

Diagnostic Criteria for HE

1. 1.Clinical evidence of hemolysis (variable; often mild or absent) ± family history
2. 2.Elliptocytes on peripheral smear (>25% of RBCs)
3. 3.Normal osmotic fragility
4. 4.Negative DAT
5. 5.Optional: Genetic testing (SPTA1, SPTB, EPB41 mutations)

First-Line Treatment

• Folic acid supplementation (1 mg daily or 5 mg three times weekly): Essential for all patients with chronic hemolysis; folic acid is consumed by compensatory erythropoiesis and becomes depleted within weeks, leading to megaloblastic anemia superimposed on hemolytic anemia; folate deficiency worsens anemia and can precipitate aplastic crisis
• Supportive care:
• Avoid medications and infections that trigger hemolysis
• Maintain hydration during infections or stress
• Treat infections promptly
• Observation alone: Sufficient for mild HS and most HE cases with Hgb >10 g/dL and no symptoms
• Blood transfusions: Reserved for symptomatic anemia (Hgb <7 g/dL, Hgb <8 g/dL with cardiovascular compromise, or acute severe hemolytic crisis); volume and frequency titrated to clinical need; chronic transfusion associated with iron overload (hemosiderosis) requiring iron chelation therapy

Second-Line Options

• Glucocorticoids: May provide temporary benefit in acute hemolytic crisis or severe acute exacerbation; do not address underlying membrane defect; taper after crisis resolves; mechanism unclear (possibly reduces splenic macrophage activity)
• **Intravenous immunoglobulin (

Complications of the disease

• **Aplastic crisis (parvovirus B19) — EMERGENCY: the virus infects erythroid progenitors (P antigen/globoside receptor) and halts erythropoiesis for ~7–10 days; in a patient whose RBC lifespan is already days rather than months, hemoglobin falls precipitously. The signal is a falling hemoglobin with an inappropriately LOW reticulocyte count** — the opposite of the baseline reticulocytosis. Distinguish from a hemolytic/sequestration crisis, in which reticulocytes rise.
• Megaloblastic crisis: chronic high-turnover erythropoiesis consumes folate; signaled by rising MCV, hypersegmented neutrophils, and worsening anemia in a patient off supplementation.
• Pigment (calcium bilirubinate) gallstones: chronic unconjugated hyperbilirubinemia; signaled by RUQ pain, and complicated by acute cholecystitis, choledocholithiasis with ascending cholangitis, or gallstone pancreatitis — cholangitis (Charcot triad) is an EMERGENCY.
• Neonatal hyperbilirubinemia / kernicterus — EMERGENCY: hemolysis plus immature UGT1A1 conjugation; the AAP hyperbilirubinemia guideline directs hour-specific bilirubin nomogram plotting, phototherapy, and exchange transfusion at escalation thresholds, with hemolytic disease treated as a neurotoxicity risk factor.
• Iron overload: from chronic transfusion (and, less often, increased absorption); signaled by rising ferritin and transferrin saturation with cardiac/hepatic/endocrine dysfunction; managed with chelation.
• Chronic sequelae: leg ulcers, growth delay, extramedullary hematopoiesis, and — in poorly controlled chronic hemolysis — pulmonary hypertension.

Complications of treatment (splenectomy)

• Overwhelming post-splenectomy infection (OPSI) — EMERGENCY: loss of splenic clearance of opsonized encapsulated organisms (S. pneumoniae, H. influenzae type b, N. meningitidis); fulminant sepsis with DIC. CDC/ACIP recommends pneumococcal, meningococcal (including serogroup B), and Hib vaccination, ideally at least 2 weeks preoperatively; the AAP Red Book supports daily penicillin prophylaxis in young children and empiric antibiotics for any fever.
• Portal/splenic vein thrombosis and reactive thrombocytosis: postoperative abdominal pain with rising platelet count.
• **Persistent spherocytes with *Howell-Jolly bodies***: expected finding confirming asplenia — not treatment failure; anemia and jaundice resolve while the membrane defect persists.

• Spherocytes + negative Coombs = hereditary spherocytosis; spherocytes + positive Coombs = warm autoimmune hemolytic anemia: this is the single most tested discrimination. The DAT is the discriminating test, because both produce identical smear morphology (splenic macrophages partially phagocytose membrane in either case).
• Elevated MCHC is the giveaway lab value: HS is one of the very few causes of a high MCHC (membrane loss shrinks surface area while hemoglobin content is preserved). A stem pairing high MCHC with reticulocytosis and jaundice is HS until proven otherwise.
• **Best next diagnostic step is *EMA (eosin-5-maleimide) binding by flow cytometry***, not the osmotic fragility test. Osmotic fragility remains the classic buzzword answer but has been largely supplanted; recognize both.
• **Sudden severe anemia with a LOW reticulocyte count = parvovirus B19 aplastic crisis**, not increased hemolysis. High reticulocytes point instead to a hemolytic or sequestration crisis. This is the most commonly tested association in HS.
• Pigment gallstones in a child, teenager, or young adult should trigger a search for chronic hemolysis; symptomatic stones warrant cholecystectomy, often performed concurrently with splenectomy.
• Splenectomy abolishes anemia but not the defect: post-splenectomy smears still show spherocytes, now accompanied by Howell-Jolly bodies (nuclear remnants no longer pitted by the spleen). Vaccination against encapsulated organisms precedes surgery per CDC/ACIP; total splenectomy is generally deferred in young children because of OPSI risk.
• Hereditary elliptocytosis is usually clinically silent — normal osmotic fragility, normal MCHC, no treatment. Its severe homozygous/compound heterozygous variant, hereditary pyropoikilocytosis, shows bizarre poikilocytes and a strikingly low MCV; Southeast Asian ovalocytosis is non-hemolytic and confers malaria resistance.
• Common distractors: G6PD deficiency (bite cells, Heinz bodies, oxidant trigger), autoimmune hemolysis (positive DAT), and PNH (intravascular hemolysis, hemoglobinuria, CD55/CD59 loss).