Triiodothyronine (T3), Free (Free T3) LabCorp

What is this test?

The Free T3 Test measures the amount of free, or unbound, T3 in the blood, which can measure thyroid health and potentially identify thyroid disease. 

T3, or Triiodothyronine, is a thyroid hormone. It is responsible for providing fuel to the body’s cells. When T3 levels are abnormally low (hypothyroidism), it causes cell dysfunction and can lead to symptoms like weight gain, constipation, dry skin, hair loss, and others. Low T3 levels may lead to the development of chronic diseases like heart disease and diabetes. When T3 levels are abnormally high, it can lead to anxiety, insomnia, heart palpitations, and bowel discomfort.

Many doctors believe that evaluating the levels of free T3 is the best indicator of thyroid function. For a full picture of thyroid health, however, this test is often combined with other thyroid-specific tests into a Complete Thyroid Panel.

Who is this test for?

This test is for anyone suffering from potential symptoms of thyroid dysfunction. This test can also be used to evaluate thyroid health in general, and to monitor ongoing management of thyroid disease in those who have already been diagnosed.