Test Description

Why get tested?

T4 free test measures the thyroxine levels in blood samples and it is one of the main tests to help diagnose hypothyroidism and hyperthyroidism. Thyroxine or T4 is one of the main thyroid hormones. Triiodothyronine (T3) and thyroxine (T4) are the most significant thyroid hormones. These hormones regulate the metabolism of the body, the process that converts food into energy.

What is being tested?

The free T4 test measures the levels of unbound T4 and this measurement is more accurate than that for bound T4. Free T4 is different from bound T4 in that free T4 enters the tissues of the body where it is required, whereas, bound T4 attaches to the proteins which prevent it from entering the tissues in the body. Free T4 circulates freely and it is not bound to proteins. 

Preparation needed?

The T4 blood test does not require specific preparation but let the doctor know if you take any supplements and medicines that may affect the result of the test.

Fasting required?

No