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TPMT Genotyping
Genetic
Report in 96Hrs
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No Fasting Required
Details
Genetic test for thiopurine metabolism.
₹7,400₹10,571
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TPMT Genotyping - Comprehensive Medical Test Information Guide
- Why is it done?
- Identifies genetic variants in the TPMT (thiopurine methyltransferase) gene that affect how the body metabolizes thiopurine medications
- Predicts individual risk for severe hematologic toxicity (bone marrow suppression) when taking thiopurine drugs such as azathioprine, mercaptopurine, or thioguanine
- Guides optimal drug dosing before initiating thiopurine therapy to minimize adverse effects and maximize therapeutic efficacy
- Ordered prior to treatment of acute lymphoblastic leukemia (ALL), inflammatory bowel disease (IBD), autoimmune conditions, and transplant rejection
- Typically performed as a pretreatment baseline test or during initial clinical assessment before thiopurine medication is started
- May be repeated if genetic status is unknown or if previous results are unavailable prior to starting thiopurine therapy
- Normal Range
- Extensive Metabolizer (EM/Wild-type): Normal alleles with normal TPMT enzyme activity; represents approximately 85-90% of the population; can tolerate standard thiopurine dosing with low risk of toxicity
- Heterozygous Intermediate Metabolizer (IM/Heterozygous): One variant allele with reduced TPMT enzyme activity; represents approximately 8-14% of the population; requires dose reduction of 25-50% due to increased toxicity risk
- Homozygous Poor Metabolizer (PM/Homozygous): Two variant alleles with severely deficient TPMT enzyme activity; represents approximately 0.3-0.6% of the population; typically contraindicated for standard thiopurine therapy or requires extreme dose reduction (80-90%) to avoid potentially life-threatening hematologic toxicity
- Interpretation: Negative/Normal = Extensive Metabolizer (EM); Abnormal = Intermediate or Poor Metabolizer phenotype indicating need for dose adjustment
- Interpretation
- Extensive Metabolizer (EM) Result: Indicates normal TPMT enzyme function; standard thiopurine dosing recommendations can be followed; patient has normal capacity to metabolize and eliminate thiopurine drugs; lower risk of medication-related bone marrow suppression
- Intermediate Metabolizer (IM) Result: Indicates reduced TPMT enzyme activity; one mutant allele affects drug metabolism; thiopurine dose should be reduced by 25-50% of standard dosing; requires closer monitoring for signs of myelosuppression; intermediate risk for adverse hematologic effects
- Poor Metabolizer (PM) Result: Indicates severe TPMT enzyme deficiency; two mutant alleles result in minimal drug metabolism capacity; substantial risk of life-threatening myelosuppression at standard doses; requires 80-90% dose reduction or consideration of alternative medications; requires intensive hematologic monitoring
- Factors Affecting Results: TPMT genotyping is not affected by medications, diet, or clinical state since it measures genetic variation; results remain consistent throughout life; ethnic background may influence allele frequency distribution
- Clinical Significance: Results directly guide pharmacologic management and prevent treatment-related morbidity and mortality; FDA recommends TPMT testing prior to azathioprine and mercaptopurine initiation; polymorphisms cause variable drug accumulation affecting therapeutic outcomes and toxicity risk
- Associated Organs
- Primary Organ Systems Involved: Hematologic system (bone marrow); liver (site of TPMT enzyme expression and drug metabolism); gastrointestinal system
- Conditions Associated with Abnormal Results: Acute lymphoblastic leukemia (ALL) requiring mercaptopurine maintenance therapy; inflammatory bowel disease (Crohn's disease, ulcerative colitis) treated with azathioprine; autoimmune disorders (rheumatoid arthritis, lupus); organ transplant recipients on azathioprine for rejection prevention; immunosuppression requirements
- Potential Complications from Abnormal TPMT Status: Severe myelosuppression and bone marrow aplasia; agranulocytosis with elevated infection risk; thrombocytopenia and hemorrhagic complications; hepatotoxicity; gastrointestinal toxicity; in poor metabolizers, potential for treatment-related death if standard dosing not adjusted
- TPMT Enzyme Function: Primarily expressed in bone marrow, liver, and red blood cells; responsible for inactivation of thiopurine drugs through methylation; reduced enzyme activity leads to drug accumulation and increased toxic metabolite formation
- Follow-up Tests
- Baseline Laboratory Tests Before Starting Thiopurine Therapy: Complete blood count (CBC) to establish baseline hematologic parameters; comprehensive metabolic panel including liver and renal function; baseline white blood cell count and differential
- Ongoing Monitoring Tests During Thiopurine Therapy: Weekly CBC for first month, then every 2-4 weeks, then every 3 months for long-term therapy; liver function tests every 3-6 months; renal function tests as clinically indicated
- Drug Level Monitoring: Thiopurine nucleotide metabolite measurement (6-TGN and 6-MMPN levels) in some clinical settings for dose optimization, particularly for poor and intermediate metabolizers
- Additional Genetic Testing: NUDT15 genotyping in some populations, particularly East Asian patients, which also affects thiopurine toxicity risk; ITPA genotyping in select cases affecting inosine triphosphatase activity
- Monitoring Frequency Recommendations: Extensive metabolizers: Standard monitoring schedule; Intermediate metabolizers: More frequent monitoring due to higher toxicity risk; Poor metabolizers: Intensive weekly to biweekly monitoring during initial dose titration phase
- Complementary Tests: Lymphocyte subset analysis for immunologic response; immunoglobulin levels for immune function assessment; inflammatory markers for disease activity monitoring in IBD or autoimmune conditions
- Fasting Required?
- Fasting Status: NO - Fasting is NOT required for TPMT genotyping
- Sample Collection Requirements: Venipuncture for blood collection (typically EDTA purple-top tube); sample can be collected at any time of day without dietary restrictions; fasting state does not affect genetic test results
- Medications to Avoid: No specific medications need to be avoided prior to TPMT genotyping; genetic testing is independent of current medication use
- Special Patient Preparation Instructions: No special preparation required; patient can eat and drink normally; test can be performed at any time; routine blood draw precautions apply (arm should be extended, relaxed); patient should remain seated for several minutes before and after venipuncture to prevent syncope
- Scheduling Considerations: Test should be completed before thiopurine therapy initiation; no time restriction for collection relative to meal times; results typically available within 5-10 business days
How our test process works!
