Thyrotropin (TSH) and free thyroxine (fT4) are the two hormones initially measured in blood to assess hypoand hyperthyroidism and to guide treatment decisions.1–3 Some guidelines and recommendations suggest specific concentrations for these hormones to guide decision making.4 Therefore, accurate and reliable TSH and fT4 tests are needed to ensure correct patient care, making the standardization of thyroid function tests to assess both thyroid gland function and therapeutic drug monitoring a priority.
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