A low serum thyrotropin level is the best test to detect thyroid dysfunction, and the highest sensitivity and specificity for the diagnosis of thyroid dysfunction.
Thyroid hormone may circulate is T3, or is T4, a prohormone, which is converted to T3 in peripheral tissues.
T3 is the physiologically active form of thyroid hormone.
Free T4 levels can be used to assess the degree of hyperthyroidism.
T3 levels can also help establish the cause and severity of
With serum TSH should be done at age 35 years and every 5 years thereafter.
More frequent screenings are appropriate for higher risk patients.
When assessing thyroid function, thyroid hormone levels, especially, free thyroxine (FT4) levels consistently show stronger associations with a wide array of clinical conditions than the measurement of thyroid stimulating hormone (TSH), according to a systematic review and meta-analysis of more than 50 studies.