TPMT thiopurine metabolites graphic

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.


Test Number Test Name
0092066 Thiopurine Methyltransferase, RBC
  • Phenotype test that assesses risk for severe bone marrow toxicity with standard dosing of thiopurine drugs
  • Performed before thiopurine therapy is initiated
  • Can detect rapid metabolizer phenotype
3001535 TPMT and NUDT15
  • Assesses genetic risk for severe bone marrow toxicity with standard dosing of thiopurine drugs
  • May be used for pre or post-therapeutic assessment


Test Number Test Name
2014484 Thiopurine Metabolites by LC-MS/MS
  • Allows clinicians to optimize therapy for thiopurine drugs
  • Identifies thiopurine metabolite concentrations that may lead to toxicity
  • May be used for post-therapeutic assessment

For additional information regarding testing strategies, refer to our Laboratory Test Directory.

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