A 24-year-old African-American man develops sudden jaundice, hemoglobinuria, and anemia three days after starting trimethoprim-sulfamethoxazole for a UTI. His hemogram shows Heinz bodies on crystal violet stain and 'bite cells' on peripheral smear. Enzyme assay confirms G6PD deficiency. Which form of G6PD enzyme is most common in affected African Americans?

• A G6PD Mediterranean (severe chronic hemolysis; Class I)
• B G6PD Canton (Southeast Asian type; Class II)
• C G6PD A+ (mild variant; normal RBC survival; Class IV)
• D G6PD A– (moderate deficiency; Class III; episodic hemolysis) ✓

Explanation

G6PD A– is the most common deficiency variant in African-American males, representing a Class III variant (~10–60% residual activity). It causes episodic acute hemolytic anemia triggered by oxidant stress (infections, drugs like dapsone, TMP-SMX, primaquine, nitrofurantoin) rather than chronic hemolysis. The enzyme is unstable, and older red cells are most deficient, so reticulocyte-rich blood (younger cells with adequate G6PD) during the acute phase can normalize the enzyme assay — 'falsely normal' result. G6PD Mediterranean (Class II) is more severe; G6PD A+ (Class IV) is a normal variant.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.