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Specimen Collection Manual and Test Catalog

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THIOPURINE S-METHYLTRANSFERASE (TPMT) GENOTYPE

Geisinger Epic Procedure Code:  LAB1357    Geisinger Epic ID:  53349

SPECIMEN COLLECTION
Specimen type: 

Whole blood


Preferred collection container: 
Alternate collection container: 
4 mL green/green-top (sodium heparin) tube
Specimen required: 

5 mL whole blood; minimum 3 mL.



SPECIMEN PROCESSING
Processing instructions: 

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.


Rejection criteria: 

Specimens received frozen.



TEST DETAILS
Additional information: 

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.


CPT code(s):  81335
Note: The billing party has sole responsibility for CPT coding.  Any questions regarding coding should be directed to the payer being billed.
The CPT codes provided by GML are based on AMA guidelines and are for informational purposes only.

Methodology: 
Polymerase Chain Reaction (PCR)
Synonyms: 

Quest test code 37742, TPMT Geno


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.


Review Date:  12/17/2024

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