Low FT3 and T3 are considered as possible hypothyroidism. FT3 refers to serum free triiodothyronine and T3 refers to triiodothyronine; hypothyroidism is an endocrine disease with decreased metabolism due to thyroid hormone insufficiency or thyroid hormone resistance, and there may be a decrease in thyroid hormone with an increase in thyrotropin. Therefore, low T3, FT3 consider the possibility of hypothyroidism. Hypothyroidism can be caused by autoimmune thyroiditis such as Hashimoto’s thyroiditis, thyroid surgery, radioactive iodine therapy and other treatments, taking medications affecting the thyroid such as lithium carbonate, hypothalamic and pituitary disorders and other factors. It is recommended to go to the hospital when you have low FT3 and T3, and ask your doctor to make a judgment and give you a treatment plan.