Skip to Main Content

Assays for FT4, total triiodothyronine (T3), and free triiodothyronine (FT3) have largely supplanted measurements of total T4, resin T3 uptake (RT3U), and free thyroxine index (FT4I). It is particularly important to determine "free" serum levels (FT4 and FT3) in conditions associated with high circulating levels of thyroxine-binding globulin (TBG), such as during therapy with oral estrogen. Ultrasensitive assays for serum TSH have largely replaced older TSH assays. Table 26–2 shows the appropriate use of thyroid tests.

Table 26–2.Appropriate use of thyroid tests.

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.