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HelpTest Code TPMT3 Thiopurine Methyltransferase Activity Profile, Erythrocytes
Specimen 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 |
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