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Thiopurine methyltransferase (TPMT)

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Also known as: TPMT RBC; TPMT Genotype; TPMT Phenotype
Formal name: Thiopurine S-methyltransferase Phenotype; Thiopurine S-methyltransferase Genotype

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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.

Sample Required?

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.