label: Abnormal circulating free T4 concentration
label_lc: abnormal circulating free t4 concentration
description: "A deviation from the normal concentration of free thyroxine (T4) in the blood circulation. Circulating T4 is almost entirely bound to specific transport proteins such as thyroxine-binding globulin (TBG) but it is the unbound (free) fraction that is able to enter tissues and exert effects."