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Test Catalog

Test ID: TPMT    
Thiopurine Methyltransferase (TPMT), Erythrocytes

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NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.


Useful For Suggests clinical disorders or settings where the test may be helpful

Detection of individuals with low thiopurine methyltransferase activity who are at risk for excessive myelosuppression or severe hematopoietic toxicity when taking azathioprine (Imuran) or 6-mercaptopurine (Purinethol)


Individuals who are either homozygous or heterozygous for thiopurine methyltransferase (TPMT) deficiency are at risk of developing life-threatening myelosuppression or severe hematopoietic toxicity when placed on standard doses of azathioprine (AZA, Imuran) or 6-mercaptopurine (6-MP, Purinethol).


Determining a patient's TPMT status prior to starting therapy with AZA or 6-MP is, therefore, important for purposes of calculating the optimal drug dosage.


There is partial overlap for the distribution of thiopurine methyltransferase activities observed between patients with normal and heterozygous genotypes. Results in the low-normal range can be due to biologic variation or assay variability.

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test

Method Name A short description of the method used to perform the test

Enzymatic End point/Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name

Thiopurine Methyltransferase, RBC

Aliases Lists additional common names for a test, as an aid in searching

TPMT (Thiopurine Methyltransferase)
Imuran Toxicity
TPMT Phenotype