This assay is used for the quantitative determination of free thyroxine (fT4) in human serum and plasma. Thyroxine (T4) is the main hormone produced by the thyroid gland and plays a crucial role in regulating metabolism, cardiovascular function, growth, bone health, and nervous system development. In circulation, only about 0.03% of T4 exists in its free, biologically active form, while the rest is bound to proteins such as thyroxine-binding globulin (TBG), pre-albumin, and albumin. Measuring free T4 provides a more accurate assessment of thyroid function, independent of fluctuations in binding proteins, making it useful in diagnosing thyroid disorders and monitoring thyrosuppressive therapy. The assay uses a homogeneous chemiluminescence immunoassay, and samples should be stored at 2–8 °C if tested within 24 hours, or frozen at -20 °C for longer storage.
