Epic Code LAB1232000 Thiopurine Methyltransferase Enzyme (TPMT) Activity

Important Note

Blood is collected prior to azathioprine (Imuran) or 6-mercaptopurine (6-MP, Purinethol) therapy for screening purposes. The draw time is at physician's discretion.

Test Name Alias

LAB10144 | Quest: 18831 | TMPT ENZYME | thiopurine methyltransferase, thiomethytransferase, 6 mercaptopurine, Thiopurine Methyltransferase(TMPT) Enzyme, Azathioprine Toxicity,Mercaptopurine Toxicity,TPMT Deficiency

Interface Order Alias

1232000

Clinical Information

TPMT Activity - 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.

Specimen Requirements

Specimen Collection Criteria

Collect (preferred specimen): Two Lavender-top EDTA tube.

Physician Office/Draw Specimen Preparation

Do not centrifuge. Refrigerate (2-8°C or 36-46°F) specimens in original collection tube immediately after collection.

In-Lab Processing

Do not centrifuge. Refrigerate (2-8°C or 36-46°F) specimens in original collection tubes immediately after collection.

Specimen Transport Temperature

Transport: Two 4.0 mL whole blood, refrigerated (2-8°C or 36-46°F). (Minimum: 2.0 mL x2). Must be shipped within 24 hours.

Rejection Criteria

Frozen specimen.
Hemolyzed specimen.
Gel separator tubes
Room temp specimen.
Specimens not collected and processed as indicated.

Specimen Stability

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 48 hours
Refrigerated (2-8°C or 36-46°F): 9 days
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.

Test Frequency

Performed: Sunday – Thursday.
Results available in 5-7 days.

Reference Range

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

Performing Department

Send Outs

Performing Department Laboratory Location

Sent to Quest Diagnostics- Wood Dale, IL

Methodology

Chromatography/Mass Spectrometry

CPT

84433

LOINC

Unavailable

Reviewed Date

11/3/2025

Orderable Regions