TPMT3 - Overview: Thiopurine Methyltransferase (TPMT) Activity Profile, Erythrocytes

Test Catalog

Test Name

Test ID: TPMT3    
Thiopurine Methyltransferase (TPMT) Activity Profile, Erythrocytes

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

Detection of individuals with low thiopurine methyltransferase (TPMT) activity who are at risk for excessive myelosuppression or severe hematopoietic toxicity when taking thiopurine drugs


Detection of individuals with hyperactive TPMT activity who have therapeutic resistance to thiopurine drugs and may develop hepatotoxicity if treated with these drugs


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), 6-mercaptopurine (6-MP, Purinethol), or 6-thioguanine (6-TG, Thioguanine Tabloid).


Individuals who have TPMT hyperactivity cannot achieve therapeutic levels with thiopurine drugs, and they may develop hepatotoxicity due to treatment with thiopurine drugs.


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

Special Instructions and Forms Library of PDFs including pertinent information and consent forms, specimen collection and preparation information, test algorithms, and other information pertinent to test

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

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

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


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

TPMT Activity Profile, RBC

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

Imuran Toxicity
TPMT (Thiopurine Methyltransferase)
TPMT Phenotype