Total Triiodothyronine
Total T3 measures all triiodothyronine in your blood, both protein-bound and free. It reflects the overall amount of this active thyroid hormone in circulation.
T3 strongly drives metabolism, and total T3 can be especially helpful in evaluating an overactive thyroid. Because most T3 is bound to proteins, the result can be affected by conditions that change those proteins. It is usually read alongside TSH and free T4.
A high total T3 often suggests an overactive thyroid, and it can be elevated in some cases where T4 appears normal. Higher binding proteins, such as in pregnancy, can also raise it. Your clinician will interpret it with your other results.
A low total T3 can occur with an underactive thyroid, but it frequently falls during illness, stress, or fasting, which does not by itself indicate thyroid disease.
A commonly cited adult range is roughly 80 to 200 ng/dL, though labs and individual factors vary. Your clinician can interpret total T3 within the broader clinical picture.
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.