Test Details: Test measures the level of T3 in the blood.T3 is the major hormone produced by the thyroid gland. T3 occurs in two forms- bound T3 (attached to protein) and free T3. Thyroid hormones play an important role in overall metabolism, body temperature regulation, weight control. T3 test is ordered if there are symptoms of hyperthyroidism such as of anxiety, weight loss, tremors, bulging eyes, fatigue, heat intolerance, etc in which T3 levels are high. Hypothyroidism is a condition in which T3 level is low.