Glucose-6-phosphate dehydrogenase deficiency testing is recommended upon entry into care or before starting therapy with an oxidant drug only in patients with human immunodeficiency virus (HIV) infection who are predisposed to this genetic disorder that can cause hemolytic anemia. Glucose-6-phosphate dehydrogenase deficiency most frequently occurs in populations of African, Asian, and Mediterranean descent and is most likely to affect HIV-infected patients with one of these racial or ethnic backgrounds.