The thyroid function is mainly based on the secretion indexes of the thyroid gland, including total T3, total T4, free T3, free T4 and TSH. The level of total T3 and T4 secretion indexes in the serum can directly reflect the functional status of the thyroid gland. In addition, TSH levels are used to determine whether the abnormalities in thyroid function are due to the thyroid gland or to the pituitary gland. In addition, some medications may affect the T3 and T4 levels in the blood. T3 and T4 may increase with estrogen therapy and birth control pills, and may decrease with medications taken for liver failure and androgenic syndrome, so there are limitations to the diagnosis of hyperthyroidism, but free T3 and T4 are not affected by these factors.