Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
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.
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.
TPMT activity is measured in RBCs. If a patient has had a recent blood transfusion, his true enzyme activity may not be accurately reflected. TPMT enzyme activity can be inhibited by several drugs such as: naproxen (Aleve), ibuprofen (Advil, Motrin), ketoprofen (Orudis), furosemide (Lasix), sulfasalazine (Azulfidine), mesalamine (Asacol), olsalazine (Dipentum), mefenamic acid (Ponstel), trimethoprim (Proloprim), methotrexate, thiazide diuretics, and benzoic acid inhibitors. TPMT inhibitors may contribute to falsely low results: patients should abstain from these drugs for at least 48 hours prior to TPMT testing. Patients with acute lymphoblastic leukemia (ALL) may have lower TPMT activities before treatment and higher activities following treatment.
- Thiopurine Methyltransferase (TPMT), Phenotype
- TPMT Enzyme
- TPMT Phenotype
- Thiopurine Methyltransferase (TPMT), Erythrocytes, Enzyme Activity
- TPMT Activity Profile
Collect specimen in a lavender top tube (preferred); green top (sodium or lithium heparin) is acceptable. Send intact whole blood, refrigerated.
If TPMT Enzyme Activity is requested, the specimen will be sent to Mayo Medical Laboratories unless the Prometheus assay is specifically requested.
Test sent to Mayo Medical Laboratories.