TPMT Activity

Test Code

18831

CPT Codes
84433

Preferred Specimen

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

Minimum Volume

2 mL (x2)

Instructions

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

Methodology
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.

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.