Trimethoprim-induced immune hemolytic anemia in a pediatric oncology patient presenting as an acute hemolytic transfusion reaction.

A 10-year-old male with acute leukemia presented with post-chemotherapy anemia. During red cell transfusion, he developed hemoglobinuria. Transfusion reaction workup was negative. Drug-induced immune hemolytic anemia was suspected because of positive direct antiglobulin test, negative eluate, and microspherocytes on smear pre- and post-transfusion. Drug studies using the indirect antiglobulin test were strongly positive with trimethoprim and trimethoprim-sulfamethoxazole but negative with sulfamethoxazole. The patient recovered after discontinuing the drug, with no recurrence in 2 years. Other causes of anemia should be considered in patients with worse-than-expected anemia after chemotherapy. Furthermore, hemolysis during transfusion is not always a transfusion reaction.