Thyroxine, also known as T4, is a hormone produced by the thyroid gland that plays a vital role in regulating metabolism and growth. The Free Thyroxine (FT4) test is a blood test that measures the amount of unbound thyroxine in the bloodstream. Unlike total thyroxine tests, which measure both bound and unbound thyroxine, the FT4 test provides a more accurate measure of the active hormone levels in the body. Abnormal FT4 levels can indicate thyroid disorders such as hypothyroidism or hyperthyroidism. The FT4 test is often performed as part of a thyroid function panel, which may also include other tests such as the Thyroid Stimulating Hormone (TSH) test. The results of the FT4 test can help doctors diagnose and monitor thyroid disorders, as well as determine appropriate treatment options.