Final answer:
TPMT deficiency is diagnosed through genetic testing or enzymatic activity assays to measure the metabolism of thiopurine drugs. TSH measurement is not used in TPMT deficiency diagnosis.
Step-by-step explanation:
Diagnosis of TPMT Deficiency
Thiopurine S-methyltransferase (TPMT) deficiency is diagnosed through various types of tests. One way to diagnose TPMT deficiency is to conduct genetic testing to identify mutations in the TPMT gene that are known to reduce enzyme activity. Another common method is through enzymatic activity assays, which measure the ability of a patient's red blood cells to metabolize thiopurine drugs. Although TSH measurement is useful for thyroid function assessment, it is not relevant to TPMT deficiency diagnosis. Unlike conditions such as Pyruvate kinase deficiency, G6PD deficiency, Lesch-Nyhan syndrome, Histidenemia, Orotic aciduria, or pyruvate dehydrogenase complex deficiency (PDCD), TPMT deficiency testing focuses on the thiopurine drug metabolism and potential myelosuppression during treatment. Genetic testing and enzymatic activity assays are critical in guiding treatment decisions, as individuals with TPMT deficiency are at increased risk of severe myelosuppression when receiving standard doses of thiopurine drugs.