Triiodothyronine - Free (FT3)

The thyroid is a small, butterfly-shaped gland located at the front of your neck. It produces a hormone called triiodothyronine, also known as T3, that helps regulate the body’s metabolism & growth, heart rate and temperature, RBC production, the development of the tissues, and the functioning of the brain. This T3 hormone, an active form of thyroid hormone, exists in the blood in two forms: free T3 (the form that is not bound to proteins) and bound T3 (the form attached to proteins). 

The Triiodothyronine - Free (FT3) test measures the free form of the T3 hormone as abnormal levels of FT3 can help detect hyperthyroidism (the thyroid gland produces too much thyroid hormone) or hypothyroidism (the gland produces less thyroid hormone). Your doctor may suggest this test if you show symptoms of hyperthyroidism, like increased appetite, weight loss, sweating, anxiety, tremors, etc., or hypothyroidism, like fatigue, weight gain, dry skin, constipation, etc. The T3-free test is also used to determine the effectiveness of thyroid medications and abnormalities of the proteins that bind thyroid hormones.

No special preparations are needed for this test. However, let your doctor know about all your medications, as some can affect thyroid function. Biotin (Vitamin B7) is a commonly taken over-the-counter supplement that can lead to some aberrancy in your thyroid test results, even if they are normal. Therefore, avoid taking biotin 2-days before this test.

Test result ranges are approximate and may differ slightly between labs depending on the methodology and laboratory guidelines. Talk to your doctor about your specific test results. The results will help them evaluate your medical condition, make recommendations for lifestyle modifications such as diet and exercise, assess whether or not medication will be required to manage your condition and formulate your overall treatment plan.