Synonyms: Free T3; T3, Free; T3, Free, Serum; Tri-iodothyronine, Free; Unbound T3

(Note: necessary lab process analysis requires 5-8 days to receive results)

Why It Is Done

This test is used to evaluate thyroid function and screen for hyperthyroidism. It is usually ordered when a patient's TSH or T4 test comes back abnormal or when a patient has signs of hyperthyroidism.

Test Overview:

Most of the T3 in the blood is attached to the thyroxine-binding globulin. Less than 1% of the T3 is unattached. A T3 blood test measure can measure both bound and free triiodothyronine. T3 has a greater effect on the way the body uses energy than T4, even though T3 is normally present in smaller amounts than T4.

How to Prepare:

No special preparation required