Thiopurine Methyltransferase (TPMT) Genotyping

CPT: 81335
Updated on 12/22/2022
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Expected Turnaround Time

7 - 10 days

7 - 10 days

7 - 10 days

7 - 10 days

7 - 10 days

Specimen Requirements


Whole blood


3 mL

Minimum Volume

1 mL (Note: This volume does not allow for repeat testing.)


Lavender-top (EDTA) tube or yellow-top (ACD) tube

Storage Instructions

Room temperature

Stability Requirements



Room temperature

28 days


28 days

Causes for Rejection

Frozen sample; hemolysis

Test Details


Detects the most common genotypes in approximately 95% of patients. Use is recommended prior to initiating thiopurine therapy.1


This assay will not detect approximately 5% of known deficiency mutations, and only the exons containing mutations in question are tested; polymorphisms or some sequence variants might affect efficiency of the PCR or mini-sequencing assays; assay does not distinguish between TPMT*1/3A heterozygote and the very rare compound heterozygote TPMT*3B/3C.

This test was developed, and its performance characteristics determined, by Labcorp. It has not been cleared or approved by the Food and Drug Administration.


Polymerase chain reaction (PCR) and multiplex mini-sequencing


1. Relling MV, Gardner EE, Sandborn WJ, et al. Clinical Pharmacogenetics Implementation Consortium guidelines for thiopurine methyltransferase genotype and thiopurine dosing. Clin Pharmacol Ther. 2011 Mar;89(3):387-391.21270794


Lennard L. Implementation of TPMT testing. Br J Clin Pharmacol. 2014 Apr;77(4):704-714.23962279


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
508080 TPMT Genetic Test 41048-0 508081 TPMT Genotype 41048-0
508080 TPMT Genetic Test 41048-0 508082 TPMT Interpretation 62365-2
508080 TPMT Genetic Test 41048-0 508083 TPMT Comment 77202-0
508080 TPMT Genetic Test 41048-0 508084 TPMT Genetic Test N/A

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