Thiopurine Methyltransferase (TPMT), Enzyme Activity, Erythrocytes

TEST: 510750
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CPT: 84433
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Synonyms

  • TPMT Biochemical Assay, Myelotoxicity

Special Instructions

For New York state patients: Test orders for TPMT Enzyme Activity 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 Enzyme Activity Test) in Related Documents.

Expected Turnaround Time

7 - 12 days

Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.

Related Documents

For more information, please view the literature below.

Therapeutic Drug Monitoring Options for Rheumatoid Arthritis Flyer

Rheumatoid Arthritis (RA) Comprehensive Testing Brochure

Informed Consent for TPMT Enzyme Activity Test

Lupus Comprehensive Testing Brochure

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

Refrigerated

14 days

Frozen

Unstable

Freeze/thaw cycles

Unstable

Causes for Rejection

Frozen specimen; gross hemolysis; clotted specimen

Test Details

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 Food and Drug Administration.

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

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 79713-4 510751 TPMT Activity Units/mL RBC 21563-2
510750 Thiopurine Methyltransferase 79713-4 510752 Interpretation: 79713-4
510750 Thiopurine Methyltransferase 79713-4 510754 Methodology 49549-9

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