Days Set Up
Monday - Friday
Analytic Time

4 days

MiChart Code
TPMT Genotype
Soft Order Code

Test Updated:


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

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Test Overview

Test Methodology

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Test Usage

Detection of individuals with low thiopurine methyltransferase activity who are at risk for excessive myelosuppression or severe hematopoietic toxicity when taking AZA and for detection of individuals with hyperactive thiopurine methyltransferase activity who have therapeutic resistance to thiopurine drugs and may develop hepatotoxicity if treated with these drugs.

Reference Range

6-Methylmercaptopurine: 3.00-6.66 nmol/mL/hr; 6-Methylmercaptopurine riboside: 5.04-9.57 nmol/mL/hr; 6-Methylthioguanine riboside: 2.70-5.84 nmol/mL/hr.

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

Specimen Requirements

Collection Onsite

Collect specimen in a lavender top tube (preferred); green top (sodium or lithium heparin) is acceptable. PLEASE NOTE: the TPMT, Erythrocytes, Enzyme Activity assays performed by Mayo Medical Laboratories (MML) and Prometheus are the same test, a quantitative measure of TPMT enzyme activity. If TPMT Enzyme Activity is requested, the specimen will be sent to Mayo Medical Laboratories unless the Prometheus assay is specifically requested. If the Prometheus assay is requested, the clinician must specify the enzyme or genetics test.

Collection Offsite

Collect specimen in a lavender top tube (preferred); green top (sodium or lithium heparin) is acceptable. Send intact whole blood, refrigerated.

Normal Volume
5 mL whole blood
Minimum Volume
3 mL 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.