TPMT Enzyme Activity Thiopurine Methyl Transferase Plasma Test

This test measures the activity of the TPMT enzyme in your blood plasma.

• It can help identify people who are at risk of developing side effects from thiopurine drugs.
• To determine the risk of bone marrow suppression caused by azathiopurine and mercaptupurine drugs
• To monitor patients on thiopurine therapy for autoimmune diseases or leukaemia
• To reduce the risk of adverse effects from thiopurine drugs
• To provide individualized drug dosages for optimal treatment outcomes

This test may be recommended if

• you have been prescribed a thiopurine drug to treat an autoimmune disease or leukaemia,
• you have experienced side effects from thiopurine drugs in the past,
• you have a history of bone marrow suppression or other blood disorders, or
• you are at high risk of experiencing bone marrow suppression due to genetic factors.

Abnormal results of the TPMT enzyme activity test suggest that a person has low TPMT activity. This means that the person's body is not able to metabolize thiopurine drugs as effectively as someone with normal TPMT activity. As a result, people with low TPMT activity are at increased risk of developing side effects from thiopurine drugs, such as bone marrow suppression.

Here are some of the possible implications of abnormal TPMT test results:

1. Need for dose adjustment: People with low TPMT activity may need to take a lower dose of thiopurine drugs than people with normal TPMT activity. This is to reduce the risk of side effects.
2. Need for alternative treatment: If a person is unable to tolerate thiopurine drugs due to low TPMT activity, their doctor may recommend an alternative treatment.
3. Increased monitoring: People with low TPMT activity may need to be monitored more closely for side effects while taking thiopurine drugs.

A trained lab technician will draw a small amount of blood from a vein in your arm. They will collect your blood sample in an EDTA (Ethylenediaminetetraacetic acid) or heparin tube and send it for testing.

• Inform your doctor about any medications that you are currently taking. Also, tell them if you have any specific requirements.
• Avoid food and drinks for at least 8 hours before the test.
• Follow your doctor's advice on stopping or continuing any medications that can interfere with the test results.

• CBC (Complete Blood Count)
• Liver Function Tests (LFTs)
• Renal Function Tests
• Genetic testing for TPMT gene mutations (TPMT genotype test)

TPMT Test, Thiopurine Methyltransferase Test, or TPMT Activity Test

Thiopurine drugs like Azathioprine and 6-Mercaptopurine are used to treat autoimmune diseases such as Crohn’s disease, rheumatoid arthritis, and leukaemia. They work by suppressing the immune system and reducing inflammation.

There are two types of TPMT tests:

1. TPMT activity test: This test measures the amount of TPMT activity in a person's red blood cells. People with low TPMT activity are at increased risk of developing side effects from thiopurine drugs, such as bone marrow suppression, which can lead to anemia, low white blood cell count, and low platelet count.
2. TPMT genotype test: This test looks for genetic variations in the TPMT gene that can affect TPMT activity. People with certain genetic variations are at increased risk of developing side effects from thiopurine drugs.