T4 Blood Test - More Information

The T4 total test, also known as a total T4 blood test, T4 total lab test, and thyroxine lab test, measures the total T4 blood level.

T4, or thyroxine, is a hormone produced by the thyroid gland. Total T4 represents the bound and unbound (free) thyroxine in the blood. Total T4 blood levels are sometimes measured along with the free T4 test to get a more thorough picture of how much T4 is in the body.

Low T4 levels are often related to hypothyroidism, or underactive thyroid function, which is why the total T4 test is included as part of the hypothyroidism test panel. High T4 blood levels are related to hyperthyroidism, or overactive thyroid function, which is why total T4 is tested as part of the hyperthyroidism test panel

Getting a T4 test near you is a fast process as standard Quest Diagnostics labs have the necessary equipment to perform the lab test. After you get your blood drawn, T4 lab results come back relatively quickly. As can be seen on the thyroxine sample report provided in the link above, T4 levels are reported as a number in mcg/dL. In addition, the lab will provide a reference range so that you can compare your total T4 results against what the lab considers to be normal.

As with any lab result, your T4 test should be interpreted in the context of any symptoms that you are having with the help of a licensed medical provider.