A 28-year-old man with a history of recurrent infections and splenomegaly presents with hemolytic anemia. His peripheral blood smear shows spherocytes and polychromasia. The direct antiglobulin test (DAT) is negative. Which investigation is most appropriate to confirm the diagnosis of hereditary spherocytosis?

Question

Accepted Answer

C. Eosin-5-maleimide (EMA) binding test. ## Diagnosis: Hereditary Spherocytosis (HS)

The clinical triad of hemolytic anemia, spherocytes on smear, and **negative DAT** (ruling out immune hemolysis) points to an intrinsic RBC membrane defect.

### Why EMA Binding Test is Most Appropriate

**Key Point:** The eosin-5-maleimide (EMA) binding test is a **flow cytometric assay** that detects defects in RBC membrane proteins (spectrin, ankyrin, band 3, protein 4.2) by measuring fluorescent dye binding.

**High-Yield:** EMA binding test is now the **gold standard** for diagnosing hereditary spherocytosis because it:
- Has **>95% sensitivity and specificity**
- Is **less operator-dependent** than osmotic fragility
- Works in all HS variants (including compensated hemolysis)
- Can detect heterozygous carriers
- Is **faster** and more reproducible than traditional osmotic fragility

**Clinical Pearl:** EMA test has largely replaced osmotic fragility in modern hematology labs due to superior performance and standardization.

### Investigation Comparison for HS Diagnosis

| Investigation | Principle | Sensitivity | Specificity | Limitations |
| --- | --- | --- | --- | --- |
| **EMA binding test** | Flow cytometry; detects membrane protein defects | >95% | >95% | Requires flow cytometer |
| Osmotic fragility test | RBC lysis in hypotonic solution | 70–80% | 90% | Operator-dependent; misses mild cases |
| Sucrose lysis test | Detects complement-mediated lysis | Low | Low | Non-specific; mainly for PNH |
| Hemoglobin electrophoresis | Separates Hb variants | N/A | N/A | Irrelevant to HS; rules out hemoglobinopathy |

**Mnemonic:** **EMA = Excellent, Modern, Accurate** — the current best test for HS.

Answer

A. Sucrose lysis test

Answer

B. Osmotic fragility test

Answer

D. Hemoglobin electrophoresis

Explanation

Diagnosis: Hereditary Spherocytosis (HS)

Why EMA Binding Test is Most Appropriate

Investigation Comparison for HS Diagnosis

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Investigation	Principle	Sensitivity	Specificity	Limitations
EMA binding test	Flow cytometry; detects membrane protein defects	>95%	>95%	Requires flow cytometer
Osmotic fragility test	RBC lysis in hypotonic solution	70–80%	90%	Operator-dependent; misses mild cases
Sucrose lysis test	Detects complement-mediated lysis	Low	Low	Non-specific; mainly for PNH
Hemoglobin electrophoresis	Separates Hb variants	N/A	N/A	Irrelevant to HS; rules out hemoglobinopathy