Also known as: Total T4; Free T4
Formal name: Thyroxine
Why should I do it?
To help evaluate thyroid gland function; to help diagnose hypothyroidism or hyperthyroidism; to screen for hypothyroidism in newborns
When should I do it?
Usually ordered in response to an abnormal TSH test result or when a person has symptoms of hyperthyroidism or hypothyroidism; commonly performed as a Screening test on newborns
What Kind of Sample is Needed?
A blood sample drawn from a vein in the arm or from pricking the heel of an infant
Test Preparation Needed?
None needed; however, certain medications can interfere with the T4 test, so tell you doctor about any drugs that you are taking.