At a Glance
Why Get Tested?
To detect a thiopurine methyltransferase (TPMT) deficiency and determine your risk of developing severe side effects if treated with the class of immune-suppressing thiopurine drugs that includes azathioprine, mercaptopurine, and thioguanine
When to Get Tested?
Typically, prior to thiopurine drug treatment; this is a specialized test and is not routinely ordered.
A blood sample drawn from a vein in your arm or a swab from inside your cheek (i.e., buccal swab)
Test Preparation Needed?
For measuring TPMT enzyme activity (TPMT phenotyping), the test must be performed prior to taking a thiopurine drug since it may affect results; for the genetic test (TPMT genotyping), no specific test preparation is needed.