TPMT Activity

Test Code

CPT Codes

Preferred Specimen
4 mL whole blood collected in two EDTA (lavender-top) tubes

Minimum Volume
2 mL (x2)

Collect venous blood in 2 separate EDTA (lavender-top) tubes (4 mL each tube). Ship at 2-8°C (refrigerated) within 24 hours of collection. Blood is collected prior to azathioprine (Imuran) or 6-mercaptopurine (6-MP, Purinethol) therapy for screening purposes. The draw time is at the physician's discretion.

Transport Temperature
Refrigerated (cold-packs)

Specimen Stability
Room temperature: 48 hours
Refrigerated: 9 days
Frozen: Unacceptable

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Hemolysis • Animal specimen • Received clotted • Forensic specimen

Chromatography/Mass Spectrometry

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: Mon-Thurs; Report available: 4-6 days

Reference Range
>12 Normal
4-12 Heterozygote or low metabolizer
<4 Homozygote Deficient Range

Clinical Significance
Help prevent hepatotoxicity from thiopurine therapy.
This test helps identify individuals at increased risk of hepatotoxicity from thiopurine dose escalation. Patients with a TMPT activity of 4-12 nmol 6-MMP/hr/mL RBC (heterozygote/low metabolizer) are at increased risk and may require a lower dose of thiopurine drug.

Performing Laboratory
Quest Diagnostics Nichols Institute-San Juan Capistrano, CA
33608 Ortega Highway
San Juan Capistrano, CA 92675-2042

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.