A patient in the hospital for a hemolytic crisis after an infection has Heinz bodies when his blood is incubated with crystal violet. The fluorescent enzyme-screening test for G6PD is normal. Select the best course of action

a. Repeat the red cell examination with new methylene blue stain.
b. Repeat the enzyme test several weeks after the hemolytic crisis.
c. Perform an osmotic fragility test.
d. Perform a haptoglobin test.

ANS: B
Reticulocytes have higher levels of G6PD than older red cells. Because reticulocytes are increased after a hemolytic episode, their presence can give a false-negative (normal) result in the screening test for G6PD. Testing should be repeated when the patient has returned to normal, with a normal cohort of red cells (all ages).