What's this test for?

This test is ideal if you're about to start a thiopurine medication (like azathioprine or 6-mercaptopurine) and want to know how your body will handle it. Some people break down these drugs slowly, which can let the medication build up to dangerous levels and damage the liver or bone marrow. Checking this ahead of time helps guide a safer starting dose.

What happens after I get my results?

Your TPMT activity result will be available in your account, along with an explanation of what the normal, reduced, and low activity ranges mean. If your result falls in the reduced-activity range, next steps typically involve starting thiopurine therapy at a lower dose and watching for signs of toxicity like unusual fatigue or bruising. The full lab report is downloadable anytime, and since this is usually a one-time baseline test, you likely won't need to retest unless instructed otherwise. If you ever have concerning symptoms after starting the medication, seek medical care right away.

Who should consider this test?

Anyone who has been prescribed a thiopurine drug, such as azathioprine, 6-mercaptopurine, or thioguanine, for conditions like inflammatory bowel disease, autoimmune disorders, or certain cancers should consider this test before starting treatment. It's especially useful if you've had bad reactions to medications in the past or have a family history of drug sensitivity. Testing beforehand can help avoid a trial-and-error approach to finding a safe dose.

What symptoms indicate I may need this test?

On its own, low TPMT activity doesn't cause symptoms — the concern is what happens after starting a thiopurine drug. Watch for signs like unusual bruising or bleeding, persistent sore throat or fever, extreme tiredness, or yellowing of the skin or eyes after beginning treatment, as these can signal the drug is building up too much. If you notice any of these, seek medical care promptly.

When will I get my results?

Results are typically ready within about 7 days of your blood draw. You'll be notified as soon as your report is available in your account, where you can view and download it anytime.

What is TPMT activity and why does it matter?

TPMT is an enzyme in your body that breaks down thiopurine drugs so they don't build up to harmful levels. Some people naturally have less of this enzyme due to their genetics, which means the drug clears more slowly and can accumulate. Knowing your activity level ahead of time helps determine a starting dose that's effective but not risky.

What does low TPMT activity mean?

Low TPMT activity (roughly 4-12 nmol 6-MMP/hr/mL RBC) means your body breaks down thiopurine drugs more slowly than average, sometimes called being a 'low metabolizer.' This raises your risk of the drug building up and causing liver or bone marrow problems if given at a standard dose. A lower starting dose with closer monitoring is usually the safer approach in this case.

What causes low TPMT activity?

Low TPMT activity is almost always due to inherited genetic variations in the TPMT gene passed down from your parents — it's not caused by diet, lifestyle, or anything you did. Roughly 1 in 10 people carry one copy of a lower-activity gene variant, and a much smaller number carry two copies, resulting in very low or absent activity. It's a naturally occurring trait, similar to blood type.

What should I do if my results are abnormal?

If your results show reduced or low TPMT activity, this information should be shared with whoever is managing your thiopurine prescription so the starting dose can be adjusted accordingly. Avoid starting or continuing the medication at a standard dose without this adjustment. Keep a copy of your report handy, since this result is relevant any time thiopurine therapy is being considered in the future.

How often should I retest?

TPMT activity is a genetic trait, so it generally doesn't change over your lifetime — this is typically a one-time test. You likely won't need to retest unless there's a specific clinical reason to confirm the result or lab methods have changed significantly.

Getting your blood test with us is easy, private & backed by the power of science.Long story short: In the test options, use the filters or search box to narrow your choices and find the test you want. If you need a hand navigating through options, text our super friendly support team at 754-799-7833, and we'll provide tailored suggestions to help you find the ideal test. Once your order is placed, we’ll create your doctor’s lab order remotely, without any need for you to make a trip to a doctor in person or to talk to the doctor. Expect to receive your doctor’s lab order right in your inbox. It will also be in your patient portal if you need to find it later. We’ll also include instructions regarding fasting and other requirements for your test. Your patient portal will be auto-created hassle-free during checkout. If this is your first time ordering, you'll be prompted to create a password for instant login access to your patient portal. It's a quick way to conveniently access your orders and results whenever you want. When you’re ready, visit one of our 4,000 locations. Just bring your ID – no printing or faxing of your lab order is needed, as your order and details will already be in the lab system. Note that most lab locations don’t accept walk-ins, so it’s best to book an appointment in advance. Don’t worry – we’ll provide detailed instructions along the way. You’ll get your results via email & SMS and dive into understanding your body better. Yup, that easy! If you have any questions, please text us at 754-799-7833 or email support@privatemdlabs.com and we'll gladly help you.

How do I know which test to get?

In the test options, find the test you want. If you’re not sure which test to get, we can lend a hand in finding the right option. Just text or call us at 754-799-7833, email us at support@privatemdlabs.com, and we'll gladly help you. We've got your back and reply quickly.

When will my lab results be available?

Most test results will be available within 1–3 business days. Once they're ready, we'll send an email and text message to let you know. After your blood draw, just hang tight and don't worry – we'll keep you updated and in the loop! If you have any further questions, please text us at 754-799-7833 or email support@privatemdlabs.com, and we'll gladly help you.

Is it possible to make changes to my lab order if I made a mistake with the name, date of birth, or any other details?

Absolutely! We totally understand that errors can happen. No worries, we're here to help you. Just reach out to us via text at 754-799-7833 or shoot us an email at support@privatemdlabs.com. Remember to include your order number and let us know the correct information you’d like to update. Our awesome team will jump right in and make sure everything is sorted out and accurate for you. There are no changes necessary if your address is wrong on the requisition though. We don’t mail anything out. Our lab requires an address to be listed to generate an order.

Do you accept health insurance?

Only HSA & FSA is accepted. Our services are strictly self-pay and cannot be submitted to your health insurance provider except for Health Savings Accounts or Flexible Savings Accounts. This policy applies to all insurance companies, including federal health insurance programs like Medicare. If you have any questions, please text us at 754-799-7833 or email support@privatemdlabs.com.

Can I cancel my order?

Yes. We get it – sometimes your needs change. As long as your samples haven’t been collected yet, we’re happy to help you cancel your order. If you have any further questions, please text us at 754-799-7833 or email support@privatemdlabs.com. You can read more about our cancellation policy here.

How can I find a lab location near me?

During the ordering process, you’ll be able to select a specific lab near you, with no strings attached! You can switch it up later easily and visit any of our authorized locations as long as it’s the same lab company you selected your test for (Quest Diagnostics or Labcorp). Before you proceed with your order, feel free to browse through all our lab locations here. This will give you the peace of mind of knowing that there's a lab nearby your home, office or your favorite gym. If you have any questions, please text us at 754-799-7833 or email support@privatemdlabs.com and we'll gladly help you.

TPMT Activity Test - Thiopurine Dosing Safety

Getting your blood test with us is easy, private & backed by the power of science.

Long story short:

In the test options, use the filters or search box to narrow your choices and find the test you want.
If you need a hand navigating through options, text our super friendly support team at 754-799-7833, and we'll provide tailored suggestions to help you find the ideal test.
Once your order is placed, we’ll create your doctor’s lab order remotely, without any need for you to make a trip to a doctor in person or to talk to the doctor. Expect to receive your doctor’s lab order right in your inbox. It will also be in your patient portal if you need to find it later. We’ll also include instructions regarding fasting and other requirements for your test. Your patient portal will be auto-created hassle-free during checkout.
If this is your first time ordering, you'll be prompted to create a password for instant login access to your patient portal. It's a quick way to conveniently access your orders and results whenever you want.
When you’re ready, visit one of our 4,000 locations. Just bring your ID – no printing or faxing of your lab order is needed, as your order and details will already be in the lab system.
Note that most lab locations don’t accept walk-ins, so it’s best to book an appointment in advance. Don’t worry – we’ll provide detailed instructions along the way.
You’ll get your results via email & SMS and dive into understanding your body better. Yup, that easy!

754-799-7833

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