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Test ID TPMT3 Thiopurine Methyltransferase Activity Profile, Erythrocytes

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

Method Name

Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name

TPMT Activity Profile, RBC

Specimen Type

Whole blood

Specimen 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.


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

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 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
TPMT3 TPMT Activity Profile, RBC 91139-6


Result ID Test Result Name Result LOINC Value
48038 Interpretation 59462-2
48034 6-Methylmercaptopurine 91141-2
48035 6-Methylmercaptopurine riboside 91142-0
48036 6-Methylthioguanine riboside 91143-8
48037 Reviewed By 18771-6


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 Client Test Request (T728) with the specimen