Thiopurine Test

TPMT Genetic Testing for Thiopurines

TPMT genetic testing identifies variants in the TPMT gene that can affect enzyme activity and response to thiopurine drugs such as azathioprine, mercaptopurine and thioguanine. Reduced or absent TPMT function is associated with an increased risk of severe myelosuppression when standard thiopurine doses are used. Genetic results can support individualized initial dosing and clinical monitoring.

Why testing is important before administering thiopurines.

The activity level of the TPMT enzyme, or the genetics behind the enzyme activity, must be tested prior to treatment with thiopurine to make sure that the subjects receiving the drugs can metabolize them.

If a person’s TPMT activity is too low, the person may not effectively metabolize thiopurines, which can lead to serious side effects.

About 1/300 subjects has severe TPMT deficiency and about 10 % of the population has lower than normal TPMT levels. Individuals in both cases are at increased risk due to drug toxicity.

This may include bone marrow suppression (myelosuppression) and/or very reduced blood cell levels such as red blood cells, white blood cells and platelets (haematopoietic toxicity). This can lead to complications such as anaemia, serious infections and/or excessive bleeding.

The test is performed on 1 EDTA vial of blood or saliva sample