The five thyroid tests, clinically referred to as the five thyroid tests, are a basic test to determine the function of the thyroid gland. It mainly includes the measurement of thyroxine T4, triiodothyronine T3, thyroid stimulating hormone TSH, free T3, and free T4. Free T3 (FT3), free T4 (FT4), and TSH are known to be among the most sensitive indicators of thyroid function, with their elevation suggesting hyperthyroidism and their decrease suggesting hypothyroidism. TSH is a sensitive indicator of the function of the hypothalamic-pituitary-thyroxine axis in the blood, and is particularly important for the diagnosis of subclinical hyperthyroidism and subclinical hypothyroidism. When a patient has lesions such as thyroid nodules and thyroid occupations, the five tests of thyroid function are the preferred tests.