Thyroid hormones regulate the body's metabolism. Thyroxine (T4) is the primary hormone produced by the thyroid gland. Most T4 circulates in the blood bound to proteins, rendering it inactive. Free T4 (FT4) refers to the small fraction of T4 that is not bound to proteins and is thus biologically active, capable of entering cells and performing its metabolic functions. Measuring FT4 provides a direct assessment of the amount of thyroid hormone readily available to body tissues. This measurement is crucial for evaluating thyroid function and detecting imbalances.
Free T4
Main circulating T4 form.