Thiopurine Methyltransferase (TPMT) Genotyping

CPT: 81335
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Expected Turnaround Time

7 - 10 days


Specimen Requirements


Specimen

Whole blood


Volume

3 mL


Minimum Volume

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


Container

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


Storage Instructions

Room temperature


Stability Requirements

Temperature

Period

Room temperature

28 days

Refrigerated

28 days


Causes for Rejection

Frozen sample; hemolysis


Test Details


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 Food and Drug Administration.


Methodology

Polymerase chain reaction (PCR) and multiplex mini-sequencing


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
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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