Question

For TPMT testing, is genotyping or phenotyping testing best to use?

1) Genotyping testing
2) Phenotyping testing
3) Both genotyping and phenotyping testing
4) Neither genotyping nor phenotyping testing

Answer 1

Genotyping is often preferred over phenotyping for TPMT testing because it provides a reliable measure that is not influenced by external factors and remains constant over time, making it more suitable for predicting adverse reactions and optimizing thiopurine dosages.

Step-by-step explanation:

For TPMT (thiopurine S-methyltransferase) testing, both genotyping and phenotyping testing can be useful, but they serve different purposes. Genotyping identifies specific genetic variants that may affect the metabolism of thiopurines, while phenotyping measures the actual enzyme activity in the patient's body. Genotyping is often preferred because it is not affected by the concurrent use of other medications or recent transfusions, and once the genotype is known, it does not change over time. Therefore, genotyping tests are considered more reliable for predicting the potential for adverse reactions or the optimal dosage of thiopurines. In the case of TPMT testing specifically to guide thiopurine therapy, genotyping is often favored because it allows for rapid analysis and identification of individuals at risk for myelosuppression when treated with standard doses of thiopurines.