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