Thiopurine Methyltransferase (TPMT) Genetic Mutation Screening (Blood)
This test checks for genetic variations in the TPMT gene that may affect how your body processes certain medications. Certain drugs used to treat conditions like leukemia or autoimmune diseases rely on TPMT activity, and low levels can increase the risk of side effects.
["Knowing your TPMT status helps doctors choose safer medication doses for you."]
Key facts at a glance
- LOINC
- 36922-3
- Short code
- TPMT gene Mut Anl Bld/T
- Synonyms
- TPMT gene Mut Anl Bld/T
- Category
- chemistry
- Sample
- whole-blood
- Container
- Lavender-top (EDTA)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- molgen
- Specimen volume
- 3 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 4–24 hours
- Order
- routine
Why This Test Matters for Medication Safety
Your TPMT genetic makeup determines how efficiently your body breaks down medications like azathioprine or 6-mercaptopurine. Some people have a genetic variant that slows this process, which can lead to higher drug levels in your blood and potential toxicity. This test helps prevent serious side effects by identifying these variations before you start treatment.
How the Test Works
A small blood sample is taken to analyze your TPMT gene. Specialized lab tests look for common mutations that affect enzyme function. Results are typically available within 1–2 weeks.
What to Expect Before the Test
No special preparation is needed for this blood test. You may have a slight bruise or soreness at the injection site, but it usually goes away quickly. If you’re pregnant, breastfeeding, or have a bleeding disorder, let your doctor know before the test.
Common Medications Affecting TPMT
Medications like azathioprine (used for immune disorders or cancer), 6-mercaptopurine (for leukemia), and some chemotherapy drugs rely on TPMT to work properly. If you’re on these or similar medications, your doctor may recommend this test to assess your risk of side effects.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: TPMT Variants and Health Risks
Short name
TPMT Gene Mutation Test
Frequently asked questions
What does a TPMT test result mean?
Can I get this test if I’m not on medication?
How long does it take to get results?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy