What is a thyroxine (T4) test?A thyroxine test helps diagnose disorders of the thyroid. The thyroid is a small, butterfly-shaped gland located near the throat. Your thyroid makes hormones that regulate the way your body uses energy. It also plays an important role in regulating your weight, body temperature, muscle strength, and even your mood. Thyroxine, also known as T4, is a type of thyroid hormone. This test measures the level of T4 in your blood. Too much or too little T4 can indicate thyroid disease.The T4 hormone comes in two forms:Free T4, which enters the body tissues where it's neededBound T4, which attaches to proteins, preventing it from entering body tissuesA test that measures both free and bound T4 is called a total T4 test. Other tests measure just free T4. A free T4 test is considered more accurate than a total T4 test for checking thyroid function.Other names: free thyroxine, free T4, total T4 concentration, thyroxine screen, free T4 concentration
