How is it used?When is it requested?What does the test result mean?Is there anything else I should know?
TPMT is either measured in patients who are about to start treatment with a thiopurine drug such as azathioprine or if the doctor suspects that the patient is experiencing side effects due to TPMT deficiency The test identifies individuals at risk of developing severe side effects such as lowering of
blood cell counts.
A doctor may requests a blood TPMT test before starting a patient on thiopurine drug treatment or if they suspect that existing side effects may be due to a deficiency of this enzyme.
What does the test result mean?
If a patient has no detectable TPMT activity then they are at risk of developing severe side effects to thiopurine drugs. Usually the doctor will find an alternative drug treatment.
A low blood TPMT activity puts the patient at risk of less serious side effects such as hair loss, stomach pain, diarrhoea and inflamation of their pancreas. In this case the doctor may reduce the dose of thiopurine drug given.
If a patient has normal blood TPMT activity then the doctor can treat the patient with a standard dose of a thiopurine drug.
Is there anything else I should know?
The TPMT enzyme activity is measured in red blood cells so if you have recently received a transfusion of blood the results of this test may be inaccurate.
