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Test Directory Thiopurine S-Methyltransferase (TPMT) Genotype

Thiopurine S-Methyltransferase (TPMT) Genotype

Test Summary

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.

Aliases

Specimen Collection

Special Instructions

N/A

Preferred Specimen

5 mL whole blood collected in an EDTA (lavender-top) tube

Minimum Volume

3 mL

Instructions

Whole blood: Normal phlebotomy procedure. Specimen stability is crucial. Store and ship room temperature immediately. Do not freeze.

Patient Preparation

N/A

Storage

N/A

Transport Temperature

Room temperature

Specimen Stability

Room temperature: 8 days
Refrigerated: 8 days
Frozen: Unacceptable

Limitations

This test detects 95% of the mutations in the TPMT gene and thus not all intermediate or slow metabolizers will be identified.

Other Acceptable Specimens

Whole blood collected in a sodium heparin (green-top), or ACD-A (yellow-top) tube

Unacceptable Specimens

N/A

Order Code

TPMTGT

EPIC (Premier) Code

LAB5218

Includes

N/A

CPT Code

81335

Billing Code

700000

CPT Statement

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 the U.S. Food and Drug Administration. The FDA has determined that such clearance or approval is not necessary. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.

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.

Testing Laboratory

Quest Diagnostics Nichols Institute
33608 Ortega Highway
San Juan Capistrano CA, 92675

Reference Range

See Laboratory Report

Setup Schedule / Expected Turnaround Time

Wednesday, Friday; Report available: 5 - 6 days