A 25-year-old woman of Mediterranean descent presents with hemolytic anemia after taking primaquine. Blood film shows Heinz bodies and bite cells. G6PD enzyme assay is normal. What is the BEST explanation for the normal assay result?
- A The patient has a different enzyme deficiency; G6PD is not involved
- B The assay was done during the acute hemolytic episode when reticulocytes with higher G6PD activity predominate, giving a falsely normal result ✓
- C G6PD deficiency only manifests as abnormal on enzyme assay between hemolytic episodes
- D Heinz bodies are not specific for G6PD deficiency and indicate unstable hemoglobin instead
Correct answer: B. The assay was done during the acute hemolytic episode when reticulocytes with higher G6PD activity predominate, giving a falsely normal result
Explanation
During acute hemolysis in G6PD deficiency, the oldest, most enzyme-depleted erythrocytes are selectively destroyed. The remaining circulating cells are relatively young (reticulocytes), which have higher G6PD activity, producing a falsely normal or near-normal enzyme assay result. Testing should be repeated 8–12 weeks after the acute episode when the red cell population has normalized to obtain a true baseline G6PD activity.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.