A 28-year-old woman of African descent presents with jaundice, dark urine, and right upper quadrant pain. She reports a recent upper respiratory tract infection 2 weeks ago. On examination, she is icteric with splenomegaly. Laboratory investigations reveal: Hemoglobin 7.2 g/dL, reticulocyte count 12%, total bilirubin 4.8 mg/dL (unconjugated 4.2 mg/dL), LDH 680 U/L, haptoglobin <10 mg/dL. Peripheral blood smear shows polychromasia and spherocytes. Direct antiglobulin test (DAT/Coombs) is negative. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Hereditary Spherocytosis ### Key Clinical Features **Key Point:** This patient presents with the classic triad of hereditary spherocytosis (HS): hemolytic anemia, jaundice, and splenomegaly, with spherocytes as the **primary and defining** finding on peripheral smear and a **negative DAT**. ### Diagnostic Reasoning | Finding | Interpretation | |---------|----------------| | **Spherocytes on smear** | Primary hallmark of HS; due to spectrin/ankyrin/band 3 defects causing membrane loss | | **Negative DAT** | Rules out autoimmune hemolytic anemia (AIHA), which also shows spherocytes but DAT-positive | | **Splenomegaly** | Characteristic of HS; spleen traps and destroys abnormal spherocytes | | **Elevated unconjugated bilirubin + LDH, low haptoglobin** | Confirms extravascular hemolysis | | **Reticulocytosis (12%)** | Compensatory bone marrow response | | **Post-URI presentation** | Infections can precipitate hemolytic crises in HS by increasing splenic activity; this is NOT exclusive to G6PD | ### Why NOT G6PD Deficiency? **High-Yield:** G6PD deficiency classically presents with: - **Bite cells and blister cells** on peripheral smear (not spherocytes as the primary finding) - **Heinz bodies** on supravital staining (precipitated denatured hemoglobin) - Hemolysis triggered by specific oxidants: drugs (primaquine, dapsone, sulfonamides), fava beans, or infections - Predominantly affects **males** (X-linked recessive); symptomatic females are uncommon - Spherocytes are **not** the characteristic or primary smear finding in G6PD deficiency ### Why NOT Autoimmune Hemolytic Anemia? AIHA also shows spherocytes but is distinguished by a **positive DAT (Coombs test)**, which is negative in this patient. The negative DAT is the critical finding that excludes immune-mediated hemolysis. ### Pathophysiology of Hereditary Spherocytosis HS results from mutations in red cell membrane skeletal proteins (spectrin, ankyrin, band 3, protein 4.2). The defective cytoskeleton leads to membrane vesiculation and loss of surface area, converting biconcave discs into spherocytes. These rigid spherocytes are trapped and destroyed in the splenic sinusoids (extravascular hemolysis), causing anemia, jaundice, and splenomegaly. **Clinical Pearl (Robbins Pathology):** Hereditary spherocytosis is the most common inherited hemolytic anemia in Northern Europeans but also occurs in other populations. The peripheral smear showing **spherocytes with a negative DAT** is the classic diagnostic combination pointing to HS over AIHA. ### Confirmatory Tests - **Osmotic fragility test**: Increased fragility (spherocytes lyse at lower osmotic stress) — hallmark of HS - **EMA (eosin-5-maleimide) binding test**: Flow cytometry-based; reduced EMA binding in HS - **Acidified glycerol lysis test (AGLT)**: Sensitive screening test - **G6PD enzyme assay**: Would be normal in HS; used to exclude G6PD deficiency **Key Point:** The combination of spherocytes + negative DAT + splenomegaly + hemolytic indices is the textbook presentation of hereditary spherocytosis (Robbins Pathologic Basis of Disease, 10th ed.).