Synonyms:

• Free T₄, Direct, Serum
• Free Thyroxine
• T₄, Free, Direct, Serum
• Unbound T₄

Free T₄ may be indicated when binding globulin (TBG) problems are perceived, or when conventional test results seem inconsistent with clinical observations. It is normal in subjects with high thyroxine-binding globulin hormone binding who are euthyroid (ie, free thyroxine should be normal in nonthyroidal diseases). It should be normal in familial dysalbuminemic hyperthyroxinemia.