A case of azathioprine-induced aplastic anemia.

Azathioprine (AZA) is an immunosuppressant that is widely used to treat many disease states including rheumatoid arthritis. We present a patient who was treated with AZA for rheumatoid arthritis and subsequently hospitalized for severe myelosuppression due to acquired aplastic anemia. Upon genetic testing it was found that the patient was thiopurine methyltransferase (TMPT) deficient, a well-documented risk factor for myelosuppression in patients taking azathioprine. We advocate for TPMT and nudix hydrolase 15 (NUDT15) testing prior to initiation of AZA treatment, or close monitoring with a complete blood count post-AZA initiation to avoid these serious side effects.