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HelpTEST ID TPMT3 Thiopurine Methyltransferase Activity Profile, Erythrocytes
Reporting Name
TPMT Activity Profile, RBCSpecimen Type
Whole bloodSpecimen Required
Patient Preparation: Thiopurine methyltransferase (TPMT) enzyme activity can be inhibited by several drugs and may contribute to falsely low results. Patients should abstain from the following drugs for at least 48 hours prior to TPMT testing: naproxen (Aleve), ibuprofen (Advil, Motrin), ketoprofen (Orudis), furosemide (Lasix), sulfasalazine (Azulfidine), mesalamine (Asacol), olsalazine (Dipentum), mefenamic acid (Ponstel), trimethoprim (Proloprim), methotrexate, thiazide diuretics, and benzoic acid inhibitors.
Container/Tube:
Preferred: Lavender top (EDTA)
Acceptable: Green top (sodium or lithium heparin), dark blue top (metal free sodium heparin), or plasma gel tubes
Specimen Volume: 5 mL
Specimen Minimum Volume
3 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole blood | Refrigerated (preferred) | 6 days | |
| Ambient | 6 days |
Special Instructions
Testing Algorithm
For more information see:
-Ulcerative Colitis and Crohn Disease Therapeutic Drug Monitoring Algorithm
-TPMT Testing in the Treatment of Inflammatory Bowel Disease Algorithm
Method Name
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Reject Due To
| Gross hemolysis | Reject |
Reference Values
6-Methylmercaptopurine (normal): 3.00-6.66 nmol/mL/hour
6-Methylmercaptopurine riboside (normal): 5.04-9.57 nmol/mL/hour
6-Methylthioguanine riboside (normal): 2.70-5.84 nmol/mL/hour
Day(s) Performed
Monday, Wednesday, Friday
Report Available
4 to 7 daysSpecimen Retention Time
Residual whole blood: 14 days; Processed specimen: 2 monthsPerforming Laboratory
Mayo Clinic Laboratories in Rochester
CPT Code Information
84433
Forms
1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. If not ordering electronically, complete, print, and send Gastroenterology and Hepatology Test Request (T728) with the specimen
Useful For
Detection of individuals with low thiopurine methyltransferase (TPMT) activity who are at risk for excessive myelosuppression or severe hematopoietic toxicity when taking thiopurine drugs
Detection of individuals with hyperactive TPMT activity who have therapeutic resistance to thiopurine drugs and may develop hepatotoxicity if treated with these drugs
Highlights
Individuals who are either homozygous or heterozygous for thiopurine methyltransferase (TPMT) deficiency are at risk of developing life-threatening myelosuppression or severe hematopoietic toxicity when placed on standard doses of azathioprine (Imuran), 6-mercaptopurine (Purinethol), or 6-thioguanine (Thioguanine Tabloid).
Individuals who have TPMT hyperactivity cannot achieve therapeutic levels with thiopurine drugs, and they may develop hepatotoxicity due to treatment with thiopurine drugs.
Determining a patient's TPMT status prior to starting therapy with a thiopurine drug is, therefore, important for purposes of calculating the optimal drug dosage.