Thiopurine Methyltransferase (TPMT) Activity
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Thiopurine Methyltransferase (TPMT) Activity/Phenotyping, Whole Blood
Test ID: TPMT
Test
Method
Enzymatic - UPLC/Fluorescence
Report Includes
Specimens
Whole Blood (EDTA)
Clinical Utility
Determining a patient’s TPMT status prior to starting therapy with a thiopurine drug is important for purposes of calculating the optimal drug dosage. Patients should be tested prior to azathioprine or 6-MP administration.
Individuals with low TPMT activity are at risk for life-threatening severe hematopoietic toxicity, while individuals with high TPMT activity present therapeutic resistance to the thiopurine drugs and may develop hepatotoxicity when taking thiopurine drugs (azathioprine, 6-mercaptopurine, or 6-thioguanine).
Test Location
Health Sciences Centre Laboratory, 820 Sherbrook Street, Winnipeg MB R3A 1R9
Test Version
10-Jan-2024
Specimen
Specimens
Whole Blood (EDTA)
Sample Volume
4 mL
Pediatric Volume
1 mL
Pediatric Minimum
0.5 mL
Patient Preparation
Total hemoglobin must be measured on the same day as collection of the TPMT specimen and submitted with the test order.
TPMT activity must be measured prior to RBC transfusion to avoid false indication.
TPMT enzyme activity can be inhibited by several drugs and may contribute to falsely low results. Patients should discontinue drugs for at least 48 hours prior to TPMT testing: naproxen, ibuprofen, ketoprofen, furosemide (Lasix), sulfasalazine (Azulfidine), mesalamine (Asacol), olsalazine (Dipentum), mefenamic acid (Ponstel), trimethoprim (Proloprim), methotrexate, thiazide diuretics, and benzoic acid inhibitors.
Collection & Handling
Handling Information
Do not centrifuge. Do not freeze. Do not transfer specimen – submit in original collection tube. Tubes with multiple overlaying labels or tubes and caps wrapped with parafilm will be rejected.
Store and send cold.
Specimen must be accompanied by a hemoglobin result determined on the same collection day. Specimen must be received at ICL Mon-Thu within 4 days of collection. State collection date.
Stability
| Refrigerated | 8 days |
|---|---|
| Frozen | Unacceptable |
Rejection Criteria
| Specimen | Frozen or centrifuged |
|---|
Test Version
10-Jan-2024
Performance / Interpretation
Method
Enzymatic - UPLC/Fluorescence
Turnaround Time
5 days
Results
| Name | Units | Reference Range | Conversion Factor | |
|---|---|---|---|---|
| Thiopurine Methyltransferase (TPMT) Activity | nmol/g Hb/h |
|
||
Test Location
Health Sciences Centre Laboratory, 820 Sherbrook Street, Winnipeg MB R3A 1R9
Test Version
10-Jan-2024
Interface / Setup
HL7 Interface Codes
| Order Code | Result Codes | Units |
|---|---|---|
| TPMT | 39162TPMT | nmol/g Hb/h |
Test Version
10-Jan-2024