Total Thyroxine
Total T4 measures all thyroxine in your blood, including both the protein-bound and the free, active portions. It reflects your overall thyroid hormone production.
T4 is the main hormone your thyroid releases, later converted into the more active T3. Because most of it is protein-bound, total T4 can shift when binding proteins change, such as in pregnancy or with estrogen. It is often interpreted alongside T3 uptake or free T4.
A high total T4 can suggest an overactive thyroid, but it may also reflect higher binding-protein levels rather than true excess hormone. Pregnancy and certain medications can raise it. Free T4 helps clarify the picture.
A low total T4 can suggest an underactive thyroid, though it may also result from low binding proteins or significant illness rather than thyroid disease itself.
A commonly cited adult range is roughly 5.0 to 12.0 mcg/dL, though this varies by lab and by conditions affecting binding proteins. Your clinician can interpret it in context.
Sources
Educational context only, not medical advice or a diagnosis. Reference ranges vary by lab, age and sex; always discuss your results with a clinician.