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Thiopurine S-Methyltransferase (TPMT) Genotype
MessageMust include Clinical Indication at time of order
Test Code
TPMT Genotype
Quest Code
37742
Alias/See Also
Thiopurine S-methyltranferase (TPMT;S-adenosyl-L-methionine:thiopurine S-methyltransferase)
CPT Codes
81335
Physician Attestation of Informed Consent
This germline genetic test requires physician attestation that patient consent has been received if ordering medical facility is located in AK, DE, FL, GA, IA, MA, MN, NV, NJ, NY, OR, SD or VT or test is performed in MA.
Preferred Specimen
5 mL whole blood collected in an EDTA (lavender-top) tube
Minimum Volume
3 mL
Other Acceptable Specimens
Whole blood collected in a sodium heparin (green-top), or ACD-A (yellow-top) tube
Instructions
Whole blood: Normal phlebotomy procedure. Specimen stability is crucial. Store and ship room temperature immediately. Do not freeze.
Transport Temperature
Room temperature
Specimen Stability
Room temperature: 8 days
Refrigerated: 8 days
Frozen: Unacceptable
Refrigerated: 8 days
Frozen: Unacceptable
Methodology
Polymerase Chain Reaction (PCR)
FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by FDA. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Setup Schedule
Set up: Wed, Fri; Report available: 5-6 days
Report Available
Maximum Laboratory Turn Around Time 8 days
Limitations
This test detects 95% of the mutations in the TPMT gene and thus not all intermediate or slow metabolizers will be identified.
Reference Range
See Laboratory Report
Clinical Significance
Thiopurine S-methyltransferase (TPMT; S-adenosyl-L-methionine:thiopurine S-methyltransferase) catalyzes thiopurine S-methylation, an important metabolic pathway for antineoplastic and immunosuppressive drugs. In the US, 11% of the population show intermediate TPMT activity, and approximately 1 in 300 have TPMT deficiency. Given potentially fatal nature of hematopoietic toxicity when full doses of mercaptopurine or azathioprine are given to TPMT deficient patients, and the difficulty to measure TPMT activity accurately when patients have been given red cell transfusions, the molecular method to determine TPMT genotype permits prospective identification of patients at risk.
Performing Laboratory
Quest Diagnostics Nichols Institute
33608 Ortega Highway
San Juan Capistrano, CA 92675-2042