1. My doctor ordered a test for thiopurine metabolites. What is it and how is it related to TPMT testing?
A doctor may order a blood test for thiopurine metabolites to monitor drug therapy. Measuring the metabolites is another way to ensure that toxic levels do not build up in the blood. Prior to administering the first dose, a doctor may test a person's TPMT enzyme activity or genotype to help determine risk of side effects as described in other sections of this article. The doctor can adjust the prescribed dose according to those results. After therapy begins, the level of metabolites can be measured and monitored, with subsequent doses adjusted as necessary to avoid toxicity.
2. What are the pros and cons of TPMT phenotyping and genotyping?
The opinions of medical organizations vary on which TPMT test to recommend. You should consult with your health care provider about which one best fits your individual situation. For example:
• The U.S. Food and Drug Administration (FDA) and prescribing information for azathioprine and mercaptopurine recommend either TPMT genotyping or phenotyping prior to thiopurine treatment.
• The American College of Gastroenterology prefers TPMT phenotyping because the phenotype assay quantifies the level of TPMT enzyme activity in patients who are being treated with thiopurines for ulcerative colitis.
This article was last reviewed on May 28, 2013. | This article was last modified on May 29, 2013.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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