Thyroxine - Total (TT4)

What is a Thyroxine (T4) test?
Thyroxine, also called thyroxine T4, is the main form of thyroid hormone made by the thyroid gland. Most of the T4 is bound to proteins, while a small proportion is unbound, or free. Free T4 testing analyses T4 that circulates throughout the blood and is also available to enter body tissues and act upon them. Total T4 testing checks the total amount of T4, including free T4 and T4 that is bound to proteins.