T3 (Triiodothyronine), Free

What is T3 Free?

T3, also referred to as Triiodothyronine, is one of the major hormones of the thyroid gland. In addition to the thyroxine hormone (T4), T3 helps the body use the energy it needs to function properly. Most of these thyroid hormones in our blood, are attached to proteins. The remaining are unbound and free: a biologically active hormone. Our thyroid gland produces, mostly, T4 hormones that are not active. But, this latter gets converted into a more active form that is T3.

To maintain the right amount of thyroid hormones, our body has a feedback system. When our body detects low levels of thyroid hormones, TSH hormone gets produced and released by the pituitary gland. TSH then stimulates the production of T4 and T3. On the other hand, when thyroid hormone levels peak in our blood, less TSH is produced leading to lower levels of T3 and T4.

The majority of T3 and T4 bind to proteins. This makes T3 hormone levels dependent upon protein levels as well as their binding powers. Free T3 levels are not affected by such protein levels.

Why take the T3 Free test?

A free T3 test is one of the best ways to assess the proper functioning of the thyroid gland. It helps diagnose hyperthyroidism, and monitors the effectiveness of a treatment targeting thyroid disorders. Free T3 can also be used to diagnose Graves disease, which could lead to hyperthyroidism.

Those who have abnormal levels of TSH, need to take the free T3 test. Those who have symptoms like fast heart rate, anxiety, weigh loss, difficulty sleeping and tremors in the hands need to get tested. Also, free T3 could be ordered if someone has diarrhea, light sensitivity, visual disturbances, weakness and puffiness around the eyes.

What can cause the levels of T3 Free to rise?

Many medications can affect the levels of free T3. Multivitamins, hair, skin and nail supplements as well as OTC medications can alter your free T3 levels.

What your T3 Free test results mean?

High levels of free T3 may indicate hyperthyroidism while low levels can mean hypothyroidism. However, this test, on its own, should not be the only diagnostic tool. Further investigations and tests need to be done.

Where can I get a T3 Free test near me?

Please use our Lab Locator to find find a convenient testing location.

References

1. American Thyroid Association. Thyroid Function Tests. Available at: https://www.thyroid.org/thyroid-function-tests/
2. American Thyroid Association. General Information/About Hypothyroidism. Available at: https://www.thyroid.org/hypothyroidism/

Reviewed By: Dr. Kurt Kloss, MD
Last Reviewed Date: May 24, 2019