Which tests are used to evaluate subclinical or subacute hyper- or hypothyroidism?

• A. FT4, FT3
• B. TSH and Total T4
• C. Calcitonin and Tg antibodies
• D. TPO antibodies and Tg antibodies

Answer: (A)

When assessing subclinical or subacute thyroid dysfunction, you need to know the level of the active hormone circulating in the body. The binding proteins in the blood can mask true hormone status if you only measure total thyroid hormones, so the most informative tests are the free forms. In subclinical disease, the pituitary adjusts TSH to keep tissues quietly supplied with thyroid hormone, so TSH may be abnormal while the free hormones stay within the normal range. Measuring free T4 and free T3 directly shows whether there is any actual excess or deficiency of circulating thyroid hormone. If free T4 and free T3 are normal, but TSH is off, that supports subclinical disease; if free hormone levels are high or low, that points to overt hyper- or hypothyroidism.

Other tests mentioned are less directly informative for this scenario. Total T4 is influenced by binding proteins and may not reflect the active hormone level as reliably. Calcitonin and Tg antibodies relate to thyroid cancer surveillance rather than current thyroid hormone status. TPO antibodies and Tg antibodies indicate autoimmune thyroid disease risk or etiology but do not by themselves define whether thyroid hormone levels are currently elevated or suppressed.