Days Set Up
Monday - Friday
Analytic Time

5 - 8 days

MiChart Code
TPMT Enzyme, Erythrocytes
Soft Order Code

Test Updated:


Thiopurine Methyltransferase (TPMT), Phenotype
TPMT Enzyme
TPMT Phenotype
Thiopurine Methyltransferase (TPMT), Erythrocytes, Enzyme Activity

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Test Overview

Test Methodology
Test Usage

Phenotypic test that provides a quantitative measurement of TPMT enzyme activity levels to assist physicians with azathioprine (Imuran) or 6-MP (Purinethol) dosing strategies. Individuals with low thiopurine methyltransferase are at risk of excessive myelosuppression.

Reference Range

Normal TPMT Activity: >21.0 EU/mL; Intermediate TPMT Activity: 6.0-21.0 EU/mL; Low TPMT Activity: <6.0 EU/mL.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Specimen Requirements

Collection Instructions

Collect specimen in a lavender top tube. Refrigerate and send intact specimen within 5 days of collection. Do not freeze.

Lavender Top Tube
Normal Volume
5 mL EDTA whole blood
Minimum Volume
2 mL EDTA whole blood

Billing Information

CPT Code
Pro Fee Code
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Our High Standard

Quality that sets us apart

As the reference laboratory division of Michigan Medicine's Department of Pathology, MLabs shares the institution's commitment to applying established quality principles to clinical laboratory testing. Like other large organizations in complex, consequential fields, we rely on an established approach to monitor quality throughout the testing process.