TPMT (Thio Purine Methyl Transferase) Gene

The TPMT blood test measures activity or genetic variants of thiopurine S‑methyltransferase to predict how a patient will metabolize thiopurine drugs (azathioprine, 6‑mercaptopurine, thioguanine). It identifies people at higher risk for severe bone marrow suppression and infections, allowing dose adjustment or alternative therapy. Testing helps personalize treatment and reduce risk of dangerous blood‑count toxicity.

A TPMT test measures activity or genetic variants of the thiopurine methyltransferase enzyme before using thiopurine drugs (azathioprine, 6‑mercaptopurine) for Crohn’s disease. It identifies people at risk of severe bone marrow suppression who need lower doses or alternative therapy. It’s done by blood enzyme assay or genetic test; normal results still require routine blood monitoring during treatment.

The TPMT gene encodes the enzyme thiopurine S‑methyltransferase, which metabolizes and inactivates thiopurine drugs (e.g., azathioprine, 6‑mercaptopurine). Variants that reduce TPMT activity cause accumulation of toxic thioguanine nucleotides, raising the risk of severe myelosuppression and other adverse effects. Genetic or enzyme testing guides thiopurine dosing to improve efficacy and reduce toxicity.

TPMT deficiency reduces metabolism of thiopurine drugs, causing buildup of toxic metabolites that often lead to severe bone marrow suppression (pancytopeni

High TPMT activity means your body rapidly inactivates thiopurine drugs (azathioprine, 6‑mercaptopurine). This lowers formation of active 6‑thioguanine nucleotides, reducing risk of bone marrow toxicity but potentially decreasing therapeutic effect. Clinically, high TPMT may prompt consideration of higher dosing, metabolite monitoring, or alternative therapies; any changes should be guided by your clinician.

TPMT testing costs vary widely by test type and location. In private labs genotyping or enzyme activity assays typically range roughly $50–$400 (₹1,000–4,000 in India), while public systems (for example the UK) generally provide it at no direct charge when clinically indicated. Insurance coverage and lab fees affect final out‑of‑pocket cost, so check with your clinic or local laboratory for exact pricing.