TPMT (thiopurine S-methyltransferase) (eg, drug metabolism), gene analysis, common variants (eg, *2, *3)
CPT4 code
Name of the Procedure:
Thiopurine S-methyltransferase (TPMT) Gene Analysis Common variants include TPMT 2 and *TPMT *3.
Summary
Thiopurine S-methyltransferase (TPMT) gene analysis is a genetic test used to determine how well a person can metabolize thiopurine medications. Variants in the TPMT gene can affect the body’s ability to process these drugs, which are used to treat certain autoimmune diseases and cancers.
Purpose
Medical Condition/Problem: Conditions requiring thiopurine medications, such as leukemia, inflammatory bowel disease, and organ transplant immunosuppression.
Goals/Expected Outcomes: Identify genetic variants that affect drug metabolism to optimize medication dosage and avoid toxic side effects or treatment failure.
Indications
- Patients with conditions treated with thiopurine medications (e.g., azathioprine, mercaptopurine).
- Individuals with known or suspected TPMT deficiency.
- Patients experiencing adverse reactions to thiopurine drugs.
Preparation
- No special preparation or fasting required.
- Inform the healthcare provider of any medications currently being taken.
Procedure Description
- Sample Collection: A blood sample or a cheek swab is obtained from the patient.
- Laboratory Analysis: The sample is sent to a lab where DNA is extracted and analyzed for TPMT gene variants (*2, *3, etc.).
- Result Interpretation: Genetic results are reviewed to determine TPMT activity level.
Tools/Equipment: Sterile collection kits, laboratory DNA analyzers.
Anesthesia/Sedation: Not applicable.
Duration
- Sample collection: A few minutes.
- Laboratory analysis: Several days to a week for results.
Setting
- Sample Collection: Outpatient clinic or laboratory.
- Laboratory Analysis: Specialized genetic testing lab.
Personnel
- Phlebotomist or nurse for sample collection.
- Geneticist or laboratory technician for DNA analysis.
- Physician or genetic counselor for result interpretation and follow-up.
Risks and Complications
- Common Risks: Minor discomfort or bruising at the blood draw site.
- Rare Risks: Infection at the blood draw site.
- Complications Management: Typically minor and manageable with standard care.
Benefits
- Personalized medication dosing.
- Reduced risk of severe side effects.
- Improved therapeutic effectiveness.
- Results are typically realized upon the next medication adjustment.
Recovery
- No recovery time needed post-sample collection.
- Follow physician's advice on medication adjustments based on test results.
- Potential follow-up appointments to monitor therapy effectiveness.
Alternatives
Empirical Dosing: Adjusting thiopurine drugs based on clinical response and side effects without genetic testing. Pros: Immediate treatment; no waiting for genetic results. Cons: Higher risk of adverse effects or ineffective treatment.
Alternative Drug Therapy: Using non-thiopurine medications. Pros: Avoids complications related to thiopurine metabolism. Cons: May be less effective or have different side effects.
Patient Experience
During Procedure: Mild discomfort from blood draw or cheek swab. After Procedure: Minimal, if any, physical sensation. Instructions primarily involve awaiting results and potential medication adjustments. Pain Management/Comfort Measures: Not generally required for the procedure itself.