Free T4 Test

Thyroid produces a hormone called thyroxine, which is known as T4. This hormone plays a role in several of our body’s functions, including growth and metabolism. Some of our T4 exists as free T4. This means it hasn’t bonded to protein in our blood. This is the type available for use by our body and tissues.

A number of drugs can interfere with your T4 levels, especially total T4, so it’s important to tell your doctor what medications you’re taking. You may need to temporarily stop taking certain drugs before the test to help ensure accurate results. It’s also important to let your doctor know if you may be pregnant.