This assay is used for the quantitative determination of free triiodothyronine (fT3) in human serum and plasma. T3, along with thyroxine (T4), is a key thyroid hormone that regulates metabolism, cardiovascular function, growth, bone health, and nervous system development. Only 0.2–0.4% of total T3 circulates as the free, biologically active form, while the rest is bound to serum proteins. Measuring free T3 is independent of protein binding variations, eliminating the need to assess binding parameters. Free T3 testing is valuable for diagnosing thyroid disorders, differentiating types of hyperthyroidism, and identifying T3 thyrotoxicosis.
