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Thiopurine Methyltransferase (TPMT), Enzyme Activity, Erythrocytes

CPT 84433
Synonyms
  • TPMT Biochemical Assay, Myelotoxicity

Test Details

Methodology

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

Result 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.

Use

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

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.

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.

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

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

Stability Requirements

Temperature

Period

Refrigerated

14 days

Frozen

Unstable

Freeze/thaw cycles

Unstable

Reference Range

• 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

Storage Instructions

Refrigerate.

Causes for Rejection

Frozen specimen; gross hemolysis; clotted specimen

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
Order Code510750
Order Code NameThiopurine Methyltransferase
Order Loinc79713-4
Result Code510751
Result Code NameTPMT Activity
UofMUnits/mL RBC
Result LOINC21563-2
Order Code510750
Order Code NameThiopurine Methyltransferase
Order Loinc79713-4
Result Code510752
Result Code NameInterpretation:
UofM
Result LOINC79713-4
Order Code510750
Order Code NameThiopurine Methyltransferase
Order Loinc79713-4
Result Code510754
Result Code NameMethodology
UofM
Result LOINC49549-9