Free T3

Triiodothyronine, known as T3, is an important thyroid hormone that regulates metabolism and ensures your body can perform essential functions properly. While most T3 in the bloodstream is bound to protein, some is unbound or free. The free T3 test measures the active form of T3 that is not bound to protein, while the total T3 test measures bound T3 and free T3 combined.

Free T3 or total T3 blood tests may be ordered to evaluate thyroid function if a thyroid disorder is suspected. They may also be used to evaluate pituitary gland problems, assess the severity and type of thyroid disease, and monitor treatment for a thyroid condition.