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Test ID GTPMT Thiopurine Methyltransferase (TPMT) Genotyping, Blood

Useful For

Predicting potential for toxicity to thiopurine drugs (6-mercaptopurine, 6-thioguanine, and azathioprine)

Reporting Name

TPMT Genotype, B

Specimen Type

Whole Blood EDTA

Specimen Required

Multiple whole blood EDTA genotype tests can be performed on a single specimen after a single extraction. See Multiple Whole Blood EDTA Genotype Tests in Special Instructions for a list of tests that can be ordered together.


Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Collection Instructions: Send specimen in original tube.

Specimen Minimum Volume

0.35 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole Blood EDTA Ambient (preferred)

Reject Due To









Reference Values

An interpretive report is provided.

Day(s) and Time(s) Performed

Monday through Friday, 8 a.m.

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

81401-TPMT (thiopurine S-methyltransferase) (eg, drug metabolism), common variants (eg, *2, *3)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
GTPMT TPMT Genotype, B 41048-0


Result ID Test Result Name Result LOINC Value
36016 TPMT Genotype Result 63454-3
36017 TPMT Interpretation 69047-9
36018 Reviewed By No LOINC Needed

Method Name

Polymerase Chain Reaction (PCR) 5'-Nuclease End-Point Allelic Discrimination Analysis


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 (Supply T576) is available in Special Instructions.

2. If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

Neurology Specialty Testing Client Test Request (T732)

Gastroenterology and Hepatology Test Request Form (T728) (