Thiopurine management

End-to-end thiopurine testing

Thiopurines are widely known as an effective treatment for patients with inflammatory bowel disease. However, many of these patients display individual variations in thiopurine metabolism, resulting in an increased risk for adverse reactions and/or a suboptimal therapeutic response.

Our end-to-end thiopurine testing was thoughtfully developed to consider genetic variations, both in individuals and certain ancestral groups, that impact metabolic response. Through special attention to diversity and equity in healthcare, our testing minimizes iatrogenic healthcare disparities in certain populations, such as Asians, Latin Americans, and Native Americans. This decreases the risk of adverse events related to medical mismanagement and medication-related toxicity.

Thiopurine management Test menu

Pre-therapy testing

Before starting patients on therapy, testing can identify individuals at risk for excessive myelosuppression or severe hematopoietic toxicity when taking thiopurine drugs (e.g., azathioprine or 6-mercaptopurine) due to low thiopurine methyltransferase (TPMT) activity.

Both enzyme and genotype testing can be performed prior to therapy initiation. Current literature does not clearly demonstrate superiority of one test over the other; however, enzyme testing can detect individuals with increased metabolism and rare variants not included in genotype testing. Research demonstrates genetic variants in Nudix hydrolase 15 (NUDT15) also affect thiopurine toxicity.1 NUDT15 can only be tested through the genotype test. Therefore, both the genotyping assay and the enzyme assay are considered complementary and are recommended.

Key testing


Testing after therapy initiation

Testing after initiation of therapy enables clinicians to optimize therapy and identify elevated metabolite concentrations that may result in toxicity. Additionally, clinicians should order testing as needed for dose changes, flare-ups, signs of toxicity, and suspicion of noncompliance, as well as in patients who do not respond to therapy as expected.

Key testing


  • Optimizes therapy through identification of elevated metabolite concentrations.
  • Facilitates understanding of therapy response when there are flare-ups, signs of toxicity, and suspicions of noncompliance.
  • Is recommended 4 weeks after starting treatment to ensure patient compliance and to look for early risk of toxicity; 12-16 weeks after beginning therapy when TGN metabolites have reached a steady state; and annually.

  1. Moriyama T, Nishii R, Perez-Andreu V, et al. NUDT15 polymorphisms alter thiopurine metabolism and hematopoietic toxicity. Nat Genet. 2016 Apr;48(4):367-73.
  2. Moyer, A. NUDT15: A bench to bedside success story. Clin Biochem. 2021;9211:1-8.

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