A patient presents with episodic hemolytic crises precipitated by infections and oxidant drugs. G6PD deficiency is suspected. Enzyme assay performed during a hemolytic crisis shows near-normal G6PD activity. What explains this finding?
- A G6PD is an inducible enzyme that is upregulated during hemolysis
- B During hemolysis, the oldest G6PD-deficient cells are preferentially destroyed; residual reticulocytes and young erythrocytes have relatively higher G6PD activity ✓
- C Hemolysis increases bilirubin which inhibits the G6PD assay chromogen
- D G6PD deficiency is compensated by upregulation of glutathione reductase
Correct answer: B. During hemolysis, the oldest G6PD-deficient cells are preferentially destroyed; residual reticulocytes and young erythrocytes have relatively higher G6PD activity
Explanation
G6PD-deficient cells show the greatest enzyme deficiency in older erythrocytes. During a hemolytic crisis, the oldest, most G6PD-deficient red cells are selectively destroyed. The surviving cells are younger reticulocytes and recently matured erythrocytes which have relatively preserved (near-normal) G6PD activity. Therefore, enzyme assays performed during or immediately after a hemolytic crisis may yield falsely normal results. Testing should be deferred 2–3 months after the acute episode for accurate diagnosis.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.