Thiopurine Methyltransferase Activity Profile, Erythrocytes
Use
Detection of individuals with low thiopurine methyltransferase (TPMT) activity who are at risk for excessive myelosuppression or severe hematopoietic toxicity when taking thiopurine drugs, and individuals with hyperactive TPMT activity who have therapeutic resistance to thiopurine drugs and may develop hepatotoxicity. This assay helps in determining a patient's TPMT status prior to starting therapy with a thiopurine drug, which is important for calculating the optimal drug dosage.
Special Instructions
Not provided.
Limitations
Thiopurine methyltransferase phenotype testing does not replace the need for clinical monitoring of patients treated with thiopurine drugs. Genotype for TPMT cannot be inferred from TPMT activity. Specimens should not be centrifuged, and several drugs may inhibit TPMT activity and cause falsely low results, requiring patients to abstain from these drugs before testing.
New York Approved
Methodology
Mass Spectrometry (LC-MS/MS)
Biomarkers
6-Methylmercaptopurine
Analyte6-Methylmercaptopurine riboside
Analyte6-Methylthioguanine riboside
Analyte
LOINC Codes
- 91139-6 - TPMT activity panel RBC
- 59462-2 - Clinical biochemist review
- 91141-2 - TPMT RBC production of 6-MMP-cCnc
- 91142-0 - TPMT RBC production 6-MMP riboside-cCnc
- 91143-8 - TPMT RBC production 6-MTG riboside-cCnc
- 18771-6 - Provider signing name
Result Turnaround Time
4-7 days
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
5 mL
Minimum Volume
3 mL
Container
Lavender top (EDTA) or Green top (sodium or lithium heparin) or dark blue top (metal free sodium heparin) or non-centrifuged plasma gel tubes
Collection Instructions
Send whole blood specimen. Do not centrifuge.
Patient Preparation
Abstain from naproxen, ibuprofen, ketoprofen, furosemide, sulfasalazine, mesalamine, olsalazine, mefenamic acid, trimethoprim, methotrexate, thiazide diuretics, and benzoic acid inhibitors for at least 48 hours prior to testing.
Causes for Rejection
Gross hemolysis
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 6 days |
| Refrigerated | 6 days |