TPMT (Thiopurine Methyltransferase) Test
About TPMT (Thiopurine Methyltransferase) Test
| Field | Value |
|---|---|
| Also Known As | Thiopurine S-Methyltransferase Test, TPMT Activity Test, TPMT Enzyme Assay, TPMT Phenotype Test, TPMT Genotype Test, TPMT RBC Test |
| Sample Type | Venous blood (whole blood in EDTA tube) |
| Fasting Required | No fasting required |
| Report Time | 3 to 5 working days (may vary by laboratory) |
| Recommended For | All individuals (male and female, any age) before starting thiopurine drug therapy |
| Price | Starting at ₹8,000 |
What Is a TPMT (Thiopurine Methyltransferase) Test?
A TPMT test measures the activity of an enzyme called thiopurine methyltransferase, which plays a key role in how the body breaks down a group of medicines called thiopurines. Doctors order this test before prescribing thiopurine drugs to check whether a patient can process these medicines safely. The sample needed is a small amount of venous blood drawn from the arm.
The test is also referred to as a Thiopurine S-Methyltransferase blood test, TPMT biochemical assay, or TPMT enzyme assay, depending on the method used.
What Does a TPMT (Thiopurine Methyltransferase) Test Measure?
The TPMT test can be performed in two ways, each measuring a different aspect of how your body handles thiopurine medicines. Here is what each approach looks at:
| Component | What It Measures | Why It Matters |
|---|---|---|
| TPMT Enzyme Activity (TPMT Phenotype Test) | The actual level of TPMT enzyme activity in red blood cells | Identifies whether enzyme activity is normal, reduced, or absent before starting therapy |
| TPMT Genetic Variants (TPMT Genotype Test / TPMT Gene Test) | Specific changes in the TPMT gene that reduce or eliminate enzyme function | Detects inherited variants (such as TPMT*2, *3A, *3B, *3C, and *4) linked to increased risk of drug toxicity |
Both the TPMT Phenotype test and TPMT Genotype test provide complementary information. In many cases, doctors order both to get a complete picture.
Why Is a TPMT (Thiopurine Methyltransferase) Test Done?
This is primarily a pre-treatment test ordered before a doctor prescribes thiopurine medicines such as azathioprine, mercaptopurine, or thioguanine.
Common Symptoms That May Require This Test
While the TPMT blood test is usually ordered before treatment begins rather than in response to symptoms, certain signs may prompt a doctor to check TPMT activity in patients already on thiopurine therapy. These include:
- Unusual bleeding or bruising
- Mouth sores or ulcers
- Unexplained fever
- Yellowing of the eyes or skin (jaundice)
- Dark or discoloured urine
- Blood in stools or urine
- Persistent fatigue or weakness
Conditions This Test Can Help Detect
The TPMT test helps identify patients at risk from thiopurine medicines. It is relevant in the following situations:
- TPMT deficiency, a condition where the body cannot adequately process thiopurine drugs
- Risk of bone marrow toxicity (suppression of blood cell production) at standard drug doses
- Possible reduced response to thiopurine therapy in patients with very high TPMT activity
- Assessment of drug toxicity risk before starting treatment for conditions such as inflammatory bowel disease, rheumatoid arthritis, haematologic cancers, and organ transplantation
TPMT (Thiopurine Methyltransferase) Test for Chronic Disease Monitoring
For patients already on thiopurine therapy for long-term conditions such as inflammatory bowel disease, rheumatoid arthritis, or post-transplant immunosuppression, the TPMT test can be repeated as needed. Doctors use it to optimise dosing, investigate signs of toxicity, assess response when doses change, or evaluate patients who are not responding to treatment as expected.
How to Prepare and What to Expect
The TPMT test requires very little preparation, but there are a few important points to keep in mind before your appointment.
Do You Need to Fast?
No fasting is required for this test. You can eat and drink normally on the day of your sample collection.
Practical Tips Before Your Test
Here are a few steps to help ensure your results are accurate:
- Tell your doctor about all medicines you are currently taking, as several common drugs can lower TPMT enzyme activity and produce falsely low results.
- Certain medicines, including sulfasalazine, mesalamine, NSAIDs, and some diuretics, may interfere with TPMT enzyme activity results. Inform your doctor about all medicines you are taking before the test.
- Phenotype (enzyme activity) testing may be less reliable in people currently taking thiopurine medicines.
- Inform your doctor if you have had a blood transfusion within the last 90 days, as this may affect enzyme activity readings.
- Wear a short-sleeved top or loose clothing for easy access to your arm.
Step-by-Step Procedure
The blood collection process is quick and straightforward. Here is what to expect:
- A trained phlebotomist will ask you to confirm your details and explain the procedure briefly
- The puncture site on your arm is cleaned with an antiseptic solution
- A soft elastic band (tourniquet) is wrapped around your upper arm to make the vein more visible
- A fine needle is gently inserted into a vein, and a small amount of blood (around 3 to 5 mL) is collected into a special EDTA tube
- The needle is removed and a small bandage or cotton pad is placed over the site
- The labelled sample is dispatched to an NABL-accredited laboratory for testing
Factors That Can Affect Accuracy
Several factors may influence how reliable your results are. These include:
- A blood transfusion received within the past 90 days
- Currently taking thiopurine drugs (for phenotype testing)
- Use of TPMT-inhibiting medicines such as certain anti-inflammatory drugs or diuretics
- Poor specimen handling or breakdown of red blood cells during transport (haemolysis)
- Impaired kidney function, which may cause falsely elevated readings
Understanding Your TPMT (Thiopurine Methyltransferase) Test Results
Your results reflect how active the TPMT enzyme is in your red blood cells. A doctor will review these findings alongside your full health history and the specific medicine being considered.
| Parameter | Range | Unit | What It Suggests |
|---|---|---|---|
| TPMT Activity (Normal) | 25 to 65 | U/mL | Standard thiopurine doses are likely to be tolerated; low risk of bone marrow toxicity |
| TPMT Activity (Low) | Below 25 | U/mL | Higher risk of bone marrow suppression at standard doses; dose reduction may be needed |
| TPMT Activity (High) | Above 65 | U/mL | Risk of reduced drug effectiveness |
Disclaimer: These ranges are general guidelines. Your doctor will interpret your results based on your age, health history, and other factors. Always consult a qualified healthcare professional for personalised medical advice.
Results During Special Conditions
Certain circumstances can alter the accuracy of a TPMT biochemical assay. Your doctor should be aware of the following:
A blood transfusion within the past three months may mask complete TPMT deficiency, as donor red blood cells may carry different enzyme activity levels. Patients already taking thiopurine medicines may show artificially raised enzyme activity due to drug-induced changes, making the phenotype test unreliable in this situation. Medicines that inhibit TPMT enzyme activity, such as sulfasalazine or ibuprofen, can produce falsely low results if not stopped before the test.
How to Support Safe Thiopurine Therapy
TPMT enzyme activity is primarily determined by your genes and cannot be changed through diet or lifestyle. However, you can take the following steps to support safe thiopurine therapy:
- Always inform every healthcare provider about your TPMT status before starting any new medicines
- Follow your doctor's dosing instructions precisely, as these will be based on your test results
- Attend all follow-up appointments so your response to therapy can be monitored over time
Lupin Diagnostics TPMT (Thiopurine Methyltransferase) Test Price and Home Collection
The TPMT test price in India starts at approximately ₹8,000, and home collection is available through Lupin Diagnostics across major cities.
| City | Approximate Price (₹) |
|---|---|
| Mumbai | ₹8,000 |
| Pune | ₹8,000 |
| Hyderabad | ₹8,000 |
| Bangalore | ₹8,000 |
| Bhopal | ₹8,000 |
| Indore | ₹8,000 |
| Chennai | ₹8,000 |
| Kolkata | ₹8,000 |
Disclaimer: Prices are indicative and may vary by location. Please confirm the current price at the time of booking.
How to Book
Select the test on the Lupin Diagnostics website
- Choose your city and preferred time slot
- Opt for home sample collection by a certified phlebotomist, or visit your nearest Lupin Diagnostics centre
- Receive your report via email or WhatsApp within the stipulated turnaround time
Home Collection
Lupin Diagnostics offers home sample collection for the TPMT test across cities in India, so you do not need to visit a centre unless you prefer to. All samples are processed in NABL-accredited laboratories, and your digital report is delivered securely via email or WhatsApp within 3 to 5 working days.
Frequently Asked Questions
The TPMT test is used to check how well your body can process a group of medicines called thiopurines, which include azathioprine, mercaptopurine, and thioguanine. Doctors order it before prescribing these drugs to identify the right dose and reduce the risk of serious side effects such as bone marrow suppression.
The TPMT Phenotype test measures the actual level of enzyme activity in your red blood cells, giving a direct reading of how your body is functioning. The TPMT Genotype test looks at your DNA to identify inherited gene variants linked to reduced or absent enzyme activity. Both tests provide useful but different information, and doctors sometimes request both together.
No fasting is required before the TPMT blood test. You can eat and drink as normal. However, you should inform your doctor about any medicines you are taking, as some can interfere with results.
Results for the TPMT test are typically available within 3 to 5 working days from the date of sample collection. Turnaround times may vary slightly depending on the laboratory and your location.
A blood transfusion within the past 60 to 120 days may affect the accuracy of the enzyme activity (phenotype) result. If you have recently had a transfusion, let your doctor know. They may recommend TPMT Genotype testing instead, as this analyses your DNA rather than red blood cell activity.
If your TPMT test shows low enzyme activity, your doctor will likely reduce the thiopurine dose significantly or consider an alternative medicine. This is a safety precaution to prevent the build-up of toxic drug levels in your body. Your response to treatment will also be monitored more closely.
The TPMT gene test (genotype) generally only needs to be done once, as your genetic make-up does not change. Enzyme activity testing may be repeated in specific circumstances, such as when there are changes in your medicines, signs of toxicity, or if you are not responding to therapy as your doctor expects.
TPMT (Thiopurine Methyltransferase) Test
