An African American male is placed on hydroxychloroquine for travel to Africa. After six weeks, he presents with anemia. What is the diagnostic study of choice in this case?

In this scenario, the patient, an African American male on hydroxychloroquine, presents with anemia after six weeks of treatment, which raises the suspicion of hemolytic anemia. Hydroxychloroquine is known to potentially induce hemolysis in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency, a hereditary condition particularly common in individuals of African descent.

The G6PD assay is the diagnostic study of choice as it directly assesses the activity of the G6PD enzyme in the red blood cells. A deficiency in this enzyme would increase the risk of hemolytic anemia when exposed to oxidative stress, such as from certain medications like hydroxychloroquine.

Other tests, such as a peripheral smear, could provide supportive evidence by showing evidence of hemolysis (e.g., reticulocytosis, bite cells, spherocytes), but they do not confirm the underlying enzymatic deficiency. Total iron binding capacity is useful in evaluating cases of iron deficiency anemia, not specifically indicated in hemolytic anemia cases like this one. Hemoglobin electrophoresis is primarily used to assess hemoglobinopathies (such as sickle cell disease or thalassemia) rather than to diagnose G6PD deficiency.