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Test Code FATPMM Thiopurine Methyltransferase (TPMT) Activity Profile, Erythrocytes

Additional Codes







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: EDTA

Acceptable: Green top (sodium heparin), metal free sodium heparin, lithium heparin, or plasma separator tubes

Specimen Volume: 5 mL

Specimen Minimum Volume

3 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole blood Refrigerated (preferred) 6 days
  Ambient  6 days

Reject Due To


Mild OK; Gross reject







Reference Values

3.00-6.66 nmol/mL/hour 6-Methylmercaptopurine (normal)

5.04-9.57 nmol/mL/hour 6-Methylmercaptopurine riboside (normal)

2.70-5.84 nmol/mL/hour 6-Methylthioguanine riboside (normal)

Day(s) and Time(s) Performed

Monday through Friday; 8 a.m.

Analytic Time

4 days (not reported on Saturday or Sunday)

Performing Laboratory

Mayo Medical 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 U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
TPMT3 TPMT Activity Profile, RBC In Process


Result ID Test Result Name Result LOINC Value
48038 Interpretation 59462-2
48034 6-Methylmercaptopurine In Process
48035 6-Methylmercaptopurine riboside In Process
48036 6-Methylthioguanine riboside In Process
48037 Reviewed By No LOINC Needed


1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

2. If not ordering electronically, complete, print, and send a Gastroenterology and Hepatology Test Request Form (T728) with the specimen (