Thiopurine Methyltransferase (TPMT)

Testing at ARUP Laboratories

Thiopurine drugs are widely used in the treatment of acute lymphoblastic leukemia (ALL), autoimmune diseases, inflammatory bowel disease, and posttransplant organ rejection. The inactivation of thiopurine drugs is primarily catalyzed by an enzyme called thiopurine methyltransferase (TPMT).

Patients with abnormal TPMT enzyme activity due to genetics and/or drug-drug interactions have an increased risk of toxicity when given thiopurine drugs.

Variants in the TPMT gene (as many as 10% of patients) can lead to low TPMT enzyme activity, resulting in accumulation of cytotoxic metabolites and increased risk for drug-related myelotoxicity with standard doses of thiopurine drugs.


For clinicians considering thiopurine drug therapy, ARUP offers a full menu of testing to support patient care.