Why is TPMT Testing Important?

• Detection of individuals with low thiopurine methyltransferase (TPMT) activity who are at risk for excessive myelosuppression or severe hematopoietic toxicity when taking thiopurine drugs.
• Detection of individuals with hyperactive TPMT activity who have therapeutic resistance to thiopurine drugs and may develop hepatotoxicity if treated with these drugs.

Available Tests and Advantages of Each

• TPNUQ — Thiopurine Methyltransferase (TPMT) and Nudix Hydrolase (NUDT15) Genotyping
  Advantages:
  • Can identify patients at risk of toxicity and start them on a reduced dose or alternate therapy
  • Test is not impacted by other medications
  • DNA is stable/specimen is less sensitive to transport conditions
  • Includes NUDT15 (three genetic variants)
• TPMT3 — Thiopurine Methyltransferase (TPMT) Activity Profile, Erythrocytes
  Advantages:
  • Can identify patients at risk of toxicity and start them on a reduced dose or alternate therapy
  • Can also detect hyperactive metabolizer
• THIO — Thiopurine Metabolites, Whole Blood
  Advantages:
  • Can adjust/optimize dose during course of therapy
  • Can monitor impact of additional drugs (i.e. allopurinol) added during course of therapy

Mayo Clinic Laboratories

This post was authored by the Marketing Team at Mayo Clinic Laboratories.