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TPMT/THIOPURINES Pharmacogenomic Lab Test

  • The TPMT genetic test screens for a gene variant of thiopurine methyltransferase (TPMT). Before starting therapy with thiopurines: azathioprine (Azasan, Imuran), mercaptopurine (Purinethol, Purixan), and thioguanine (Tabloid), Mayo Clinic recommends testing for the TPMT gene variant.

  • If your test results show you have a reduced capacity to process thiopurines, talk with your healthcare provider about your options.

  • If your test results show you process thiopurines at a normal rate, a standard dose will generally be suggested.

Your health care provider evaluates your test results and uses this information, along with your other health information, to make recommendations for appropriate treatment options.

TPMT Test Results

What should I do with my test results?

Talk to your health care provider or pharmacist about the results. They may suggest that you:

  • Keep taking a medication
  • Change the dose of a medication
  • Stop taking a medication
  • Take a different medication

Are there multiple TPMT tests?

Two different lab tests are used to help your health care provider determine how you process (metabolize) thiopurines. The TPMT Enzyme test below measures the enzyme activity in your blood. The TPMT Genetic test uses genetic information to determine how you process (metabolize) thiopurines. The information below helps you understand the test results.

What does my Thiopurine methyltransferase (TPMT) Enzyme test result mean?

Deficient/Low or Thiopurine Methyltransferase Deficient

This means that your body does not process (metabolize) thiopurines well. Your healthcare provider may either suggest that you take a very low dose of the medication, or they may suggest a different medication.

Intermediate, Carrier, or Low Normal

This result means that your body processes (metabolizes) thiopurines slower than normal. Your healthcare provider will generally suggest a lower dose of thiopurines.

Normal

Your body is able to process (metabolize) thiopurines normally. A standard dose of thiopurines will generally be suggested.

What does my Thiopurine Methyltransferase (TPMT) Genetic test mean?

Poor

This means that your body does not process (metabolize) thiopurines well. Your healthcare provider may either suggest that you take a very low dose of the medication, or they may suggest a different medication.

Intermediate

This result means that your body processes (metabolizes) thiopurines slower than normal. Your healthcare provider will generally suggest a lower dose of thiopurines.

Extensive

Your body is able to process (metabolize) thiopurines normally. A standard dose of thiopurines will generally be suggested.

Who will see my results?

Only health care professionals, and those you have given permission, may view your genetic test results. If you are receiving care at another medical facility, we suggest you share this information with your other health care providers.

What are thiopurines?

Thiopurines: Azathioprine (Azasan and Imuran), Mercaptopurine (Purinethol, Purixan), and Thioguanine (Tabloid) are medications widely used to treat leukemias and autoimmune disorders such as inflammatory bowel disease (Crohn's disease and ulcerative colitis) and arthritis. They also are used after organ transplantation to prevent organ rejection, and for some dermatologic conditions.

How could the TPMT test result affect my treatment?

If testing shows that you have a TPMT variant that reduces your ability to process (metabolize) a thiopurine, your provider may prescribe a different drug or change the dose of your current medication.

Who is affected? Do different populations respond differently?

TPMT variants are found in all populations.

What are thiopurines?

Thiopurines: Azathioprine (Azasan and Imuran), Mercaptopurine (Purinethol, Purixan), and Thioguanine (Tabloid) are medications that are widely used to treat leukemias and autoimmune disorders such as inflammatory bowel disease (Crohn's disease and ulcerative colitis) and arthritis. They are also used after organ transplantation to prevent organ rejection.

Which gene affects my response to thiopurine medications?

Variants in a gene called thiopurine methyltransferase (TPMT) influence the way that your body processes (metabolizes) thiopurines and can affect your response to this medication.

What problems can patients with TPMT variants have when taking a thiopurine drug?

Patients who have a TPMT gene variant process (metabolize) thiopurine medications more slowly and can have serious side effects.

Patients may have symptoms, such as bleeding, sores, fever, bruising, yellowing eyes/skin, discolored urine and stool, and bloody urine and stool.

Other considerations:

If you are currently taking thiopurines and not having problems, pharmacogenomic testing may not be needed.

Where can I find more information about thiopurine methyltransferase and pharmacogenomics?

These resources may help you understand more about individualized medicine, genomics and drug-gene testing (pharmacogenomics):

If you have questions about your test results, ask to speak with your health care provider at your Mayo Clinic care location:

  • Minnesota 507-284-2511

  • Arizona 480-301-8000

  • Florida 904-953-2000