What is a T4 test?
Thyroxine (T4) is a hormone produced by the thyroid gland. The thyroid is a butterfly-shaped gland that lies below your Adam’s apple in the front of the neck. The gland is responsible for the production of the triiodothyronine (T3) and thyroxine (T4) hormones, which regulate your body’s metabolism and growth. T4 tests are used to determine the levels of the thyroxine hormone you have in your body. Too much or too little T4 can indicate a problem with your thyroid gland such as hyperthyroidism or hypothyroidism.