Triiodothyronine, or T3, is an important thyroid hormone that helps maintain muscle control, brain function and development, heart and digestive functions. High or low T3 levels may indicate an ...

A blood test can check the amount of hormones that your thyroid is making. Many factors can affect these levels. (Photo credit: Jarun011/Dreamstime) A TSH test is done to find out if your thyroid ...