Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.
People who have thyroid hormone resistance syndrome may experience abnormal free T3 or total T3. If the If anti-thyroid medication is effective to treat hyperthyroidism, the free or total T3 may stay normal. If the medication is not effective, then the free or total T3 or free T4 may elevated.
Increased or decreased thyroid hormone results indicate that there is an imbalance between the body's requirements and supply, but they do not tell the health practitioner specifically what is causing the excess or deficiency.
High free T3 may indicate hyperthyroidism, or mild (subclinical) hyperthyroidism.
Low free T3 may indicate non-thyroidal illness, rare pituitary (secondary) hypothyroidism.