Free thyroxine (Free T4) is used to evaluate thyroid function independent of binding protein status. The test measures serum thyroxine (T4) that is not bound to thyroid hormone-binding proteins (thyroid hormone-binding globulin [TBG], transthyretin, albumin) and is thus readily available to target cells. This test is used with thyroid-stimulating hormone measurement in the diagnosis of hyperthyroidism and hypothyroidism (low FT4), including congenital and acquired hypothyroidism.

Synonyms: FT4

SST, Serum. Volume 1 (0.5) mL serum. Stability: Refrigerated – 4 Days, Frozen – 2 Months