Triiodothyronine - Total (T3)

Triiodothyronine, also known as T3, is a hormone produced by the thyroid gland. The thyroid is a small, butterfly-shaped gland located at the front of your neck. It helps regulate the body’s metabolism and growth, heart rate, temperature, and the development of tissues. T3 along with thyroxine (T4), another hormone produced by the thyroid gland, plays an important role in the growth and development of the nervous system and the brain. T3 is the active form of thyroid hormone that 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). More than 99% of the T3 is in the bound form; only a small proportion is free and not attached to proteins.

The Triiodothyronine - Total (T3) test measures the total level (both free and bound forms) of the T3 hormone in the blood. Abnormal levels of T3 hormone can result in either hyperthyroidism (the thyroid gland produces too much T3) or hypothyroidism (the gland produces less T3). 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.

No special preparations are needed for the Triiodothyronine - Total (T3) test. However, let your doctor know about all the medications you take as some of them 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 different 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.