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Test Code
TPMGN
Test Name
TPMT Genotype
CPT Codes
81335
Expected Turnaround Time
6 - 7 days
Clinical Utility
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.
Specimen and Container Info

Specimen Type: Whole Blood

  

Collection Container: Pale Yellow Top (ACD A or B)

Alternate Collection Container: Lavender Top (EDTA) or Green Top (Sodium Heparin)

Desired Specimen Volume: 5 mL
Collection Instructions
  1. Collect a pale-yellow top (ACD A or B) tube via venipuncture.
Processing and Submission Instructions
  1. Transport 5 mL of whole blood in the original collection container.
Transport Instructions

Transport to the laboratory at room temperature.  
Stability Requirements

Room Temperature

8 days

Refrigerated

8 days
Methodology
Polymerase Chain Reaction
Reference Intervals

See patient report.
Alternate Names
  • Azathioprine Toxicity
  • Mercaptopurine Toxicity
  • TPMT Deficiency
Reference Lab
Quest Diagnostics Nichols Institute
Testing Schedule
Varies
The American Medical Association (AMA) Current Procedural Terminology (CPT) codes published by HNL Lab Medicine are guidelines and are intended for informational purposes only. CPT coding is the exclusive responsibility of the billing entity. View the Terms.
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