Thiopurine Methyltransferase (TPMT), Enzyme Activity, Erythrocytes

CPT: 82657
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Test Details

Synonyms

  • TPMT Biochemical Assay, Myelotoxicity

Use

Determination of TPMT levels that may be associated with toxicity of anticancer and anti-inflammatory drugs

Limitations

For patients having an intrinsic low level of TPMT, recent RBC transfusion can variably increase their assayed enzymatic activity depending on the amount and circulating half-life of the transfused red blood cells.

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

Enzymatic endpoint/liquid chromatography/tandem mass spectrometry (LC/MS-MS).

Reference Interval

• Normal: 15.1−26.4 units/mL RBC

• Heterozygous for low TPMT variant: 6.3−15.0 units/mL RBC

• Homozygous for low TPMT variant: <6.3 units/mL RBC

Specimen Requirements

Specimen

Whole blood

Volume

8 mL adults; 5 mL pediatric

Minimum Volume

5 mL

Container

Green-top (sodium heparin) tube or lavender-top (EDTA) tube

Storage Instructions

Refrigerate.

Stability Requirements

Temperature

Period

Room temperature

2 days

Refrigerated

14 days

Frozen

Unstable

Freeze/thaw cycles

Unstable

Causes for Rejection

Frozen specimen; gross hemolysis

Clinical Information

References

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

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
510750 Thiopurine Methyltransferase 510751 TPMT Activity Units/mL RBC 21563-2
510750 Thiopurine Methyltransferase 510752 Interpretation: 79713-4
510750 Thiopurine Methyltransferase 510754 Methodology 49549-9
510750 Thiopurine Methyltransferase 501133 TPMT N/A

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