Which is Best for TPMT Testing: Genotyping or Phenotyping?

Explanation:

TPMT Testing Overview: TPMT testing is used to assess an individual's ability to metabolize thiopurine medications, such as azathioprine, mercaptopurine, and thioguanine. These medications are commonly used to treat autoimmune diseases, such as inflammatory bowel disease and rheumatoid arthritis.

Genotyping vs. Phenotyping: Both genotyping and phenotyping testing can be utilized for TPMT testing, but they serve different purposes. Genotyping identifies specific genetic variants that may affect thiopurine metabolism, while phenotyping measures the actual enzyme activity in the patient's body.

Advantages of Genotyping: Genotyping is often preferred over phenotyping for TPMT testing because it is not influenced by external factors, such as concurrent medication use or recent transfusions. Once an individual's genotype is known, it remains constant over time, providing a reliable basis for predicting adverse reactions and determining optimal thiopurine dosages.

Role in Thiopurine Therapy: When TPMT testing is utilized to guide thiopurine therapy, genotyping is typically favored due to its rapid analysis and ability to identify individuals at risk for myelosuppression when treated with standard doses of thiopurines. This allows healthcare providers to adjust dosages and minimize the potential for adverse reactions.

Overall, genotyping testing is often considered the preferred method for TPMT testing, as it offers a reliable and consistent measure for predicting patient responses to thiopurine medications.