Specimen Requirements


Thiopurine Metabolites (6-TG/6-MMP)

Specimen Requirement

Collect a full lavender EDTA within 1 hour prior to the next dose (trough required), send whole blood refrigerated.


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


Room Temp: 24 Hours; Refrigerated: 5 days

Reference Range



4-6 days Performed Tuesday-Saturday

Clinical Use

Test includes: 6-Thioguanine (6-TG) and 6-Methylmercaptopurine (6-MMP)

6-Mercaptopurine (Purinethol) and its imidazolyl derivative, Azathioprine (Imuran), are immunosuppressive drugs. 6-Mercaptopurine (6-MP) is indicated for remission induction and maintenance therapy of acute lymphoblastic leukemia (ALL). Azathioprine is indicated as an adjunct for the prevention of rejection in renal allograft (kidney transplant) patients, for the management of rheumatoid arthritis, and for the management of inflammatory bowel disease.
Azathioprine is cleaved to 6-MP. 6-MP is metabolized via a series of enzymatic steps to 6-thioguanine nucleotides (6-TGNs), to 6-methyl-mercaptopurine (6-MMPNs) by the enzyme thiopurine methyltransferase (TPMT), and to 6-thiouric acid by the enzyme xanthine oxidase (XO). TPMT enzyme activity has large inter-individual variations which affect the efficacy, toxicity and variability of the treatment. Therapeutic drug monitoring of 6-MP metabolites (6-TGNs and 6-MMPNs) in erythrocytes is recommended to assist therapy, particularly in combination with TPMT enzyme activity or mutation analysis.

Test Code