A 35-year-old man of African descent develops acute intravascular hemolysis following primaquine therapy. His G6PD enzyme assay performed during the acute hemolytic episode appears near-normal. The most likely explanation for this near-normal result is:

• A G6PD deficiency has been corrected by the oxidant stress
• B The primaquine dose was insufficient to cause true G6PD deficiency
• C Older G6PD-deficient RBCs have been destroyed; reticulocytes and young RBCs present have relatively higher G6PD activity ✓
• D G6PD enzyme activity is upregulated during hemolytic crisis

Explanation

The African (A-) variant of G6PD deficiency is characterized by an enzyme with accelerated decay — older RBCs have very low G6PD activity while young RBCs (reticulocytes) maintain near-normal levels. During an acute hemolytic episode, the older G6PD-deficient cells are selectively destroyed, leaving a pool of younger cells with higher activity. Testing during the hemolytic episode gives falsely normal results. Testing should be delayed 2-3 months after the episode. The Mediterranean variant has more severe deficiency affecting all RBC ages.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.