Thiopurine Methyl Transferase RBC
Referred to external laboratory.
Thiopurine methyltransferase (TPMT) enzyme activity is measured in patients prior to starting treatment with a thiopurine drug. When TPMT activity is low, a genetic test is also performed. These results are used to identify individuals at risk of toxicity from thiopurine therapy. TPMT is not useful in monitoring azothiopurine levels and 6TGN is the preferred test.