Our global life sciences company brings diagnostic testing & drug development together.

Thiopurine Methyltransferase (TPMT) Genotyping

CPT: 81335
Updated on 08/31/2021
Print Share


  • TPMT Genetic Testing

Special Instructions

Test orders for TPMT Genotyping must include an attestation that the provider has the patient's informed consent for genetic testing. See sample physician office consent form (Informed Consent for TPMT Genetic Testing) in Related Documents.

Expected Turnaround Time

7 - 15 days

6 - 10 days

7 - 15 days

Related Documents

Specimen Requirements


Whole blood or LabCorp buccal swab (buccal swab collection kit)


3 mL

Minimum Volume

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


Lavender-top (EDTA) tube, yellow-top (ACD) tube, green-top (heparin) tube, or LabCorp buccal swab (from kit)

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 US Food and Drug Administration (FDA).


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
504142 TPMT Genetic Test 41048-0 504144 TPMT Genotype 41048-0
504142 TPMT Genetic Test 41048-0 504145 TPMT Interpretation 62365-2
504142 TPMT Genetic Test 41048-0 504146 TPMT Comment 77202-0
504142 TPMT Genetic Test 41048-0 504143 Background 36922-3

For Providers

Please login to order a test

Order a Test

© 2021 Laboratory Corporation of America® Holdings and Lexi-Comp Inc. All Rights Reserved.

CPT Statement/Profile Statement

The LOINC® codes are copyright © 1994-2021, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at Additional information regarding LOINC® codes can be found at, including the LOINC Manual, which can be downloaded at