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TPMT Testing Before Azathioprine — ESENeph MCQ

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EasyRenal VasculitisTPMT Testing Before AzathioprineESENeph

A 40-year-old man with ANCA-negative pauci-immune crescentic GN has been treated with Cyclophosphamide and Glucocorticoids. After achieving remission, he is transitioned to maintenance Azathioprine. Before starting Azathioprine, what pharmacogenomic test should be performed?

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Correct answer: D — TPMT (thiopurine methyltransferase) activity testing – deficiency increases risk of severe myelosuppression from Azathioprine

TPMT (thiopurine methyltransferase) is the key enzyme in Azathioprine/6-mercaptopurine metabolism. Approximately 10% of the population has intermediate TPMT activity and ~0.3% has absent activity. Absent TPMT causes life-threatening myelosuppression at standard Azathioprine doses. NICE, BNF, and KDIGO recommend TPMT testing before starting Azathioprine. Patients with absent activity should not receive Azathioprine. Those with intermediate activity may tolerate reduced doses with close FBC monitoring.

Reference: BNF 2024 – Azathioprine; NICE – TPMT Testing Recommendation