The free T3 count, also called free triiodothyronine, is an estimate of the amount of triiodothyronine hormone that is unbound or accessible in the circulation. Triiodothyronine (T3) is one of the thyroid gland’s two principal thyroid hormones, the other being thyroxine (T4).

A low free T3 count can suggest a number of diseases, including:

• Hypothyroidism is the most prevalent cause of a low free T3 concentration. Hypothyroidism is a disorder in which the thyroid gland is underactive.
• Certain medicines or therapies, such as beta-blockers and antithyroid agents, can restrict the generation or conversion of T3, resulting in low free T3 levels. Thyroid hormone production can also be affected by therapies such as radioactive iodine therapy or thyroid surgery.
• Non-thyroidal disease or stress: Nonthyroidal illnesses or extreme stress can induce changes in thyroid hormone levels in some people. This is characterized as “low T3 syndrome” or “euthyroid sick syndrome.”

Hyperthyroidism can be caused by a number of illnesses, including Graves’ disease, toxic multinodular goiter, and thyroiditis. Weight loss, increased hunger, fast pulse, palpitations, anxiety, irritability, heat intolerance, tremors, sweating, and changes in bowel habits are all symptoms of hyperthyroidism.