Thiopurine Methyltransferase (TPMT) Genotyping

CPT: 81401
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Test Details

Synonyms

  • TPMT Genetic Testing

Use

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

Limitations

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).

Methodology

Polymerase chain reaction (PCR) and multiplex mini-sequencing

Specimen Requirements

Specimen

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

Volume

3 mL

Minimum Volume

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

Container

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

Storage Instructions

Room temperature

Causes for Rejection

Frozen sample; hemolysis

Clinical Information

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.

Footnotes

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

References

Lennard L. Implementation of TPMT testing. Br J Clin Pharmacol. 2014 Apr; 77(4):704-714. 23962279

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
504142 TPMT Genetic Test 504144 TPMT Genotype 41048-0
504142 TPMT Genetic Test 504145 TPMT Interpretation 62365-2
504142 TPMT Genetic Test 504146 TPMT Comment 77202-0
504142 TPMT Genetic Test 504143 Background 36922-3
504142 TPMT Genetic Test 504147 TPMT Genetic test N/A

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