Understanding the state of pharmacogenomic testing for thiopurine methyltransferase within a large health system.

To investigate the current state of TPMT testing at a single-academic medical center. Single-center, retrospective chart review for patients newly prescribed a thiopurine. Data collection and evaluation included the prevalence and timing of TPMT testing, correct dosage adjustment if applicable, and incidence of myelosuppression. 121 patients (71%) received TPMT testing. Out of the tested patients, 110 (90.9%) were designated as wild-type with normal metabolism. Dosing modification was appropriate in applicable patients. In unadjusted analysis, there was a lower incidence of myelosuppression among patients who were tested versus those who were not (16.5 vs 36.7%). Based on the study results, TPMT testing opportunities exist for nearly 30% of patients. Testing may reduce the incidence of myelosuppression.