The five items of thyroid function generally refer to serum TSH thyroid stimulating hormone, TT4 serum total thyroxine, TT3 serum total triiodothyronine, FT3 free triiodothyronine, FT4 free thyroxine, but different hospitals may have different check items. 1. Serum TSH: It is the most commonly used, reliable and sensitive test for evaluating thyroid function; TSH is the most sensitive indicator for diagnosing hypothyroidism. 2. Serum TT3, TT4: Determination of TT3 and TT4 can directly understand the function of the thyroid gland, but due to the level of both are affected by the concentration of thyroid-binding globulin in the blood, which limits the value of its clinical application; however, it has its special role for T3-type or T4-type hyperthyroidism. 3. Serum FT3 and FT4: FT3 and FT4 exist in free state in the blood, representing the level of thyroid hormones in the tissues, which is consistent with the metabolic state of the body and is not affected by thyroid-binding globulin; they are used to diagnose hyperthyroidism and hypothyroidism, and to monitor the thyroid function in the course of treatment; in the diagnosis of hyperthyroidism, the value of FT3 and FT4 is higher than that of TT3 and TT4. It is recommended that patients go to regular hospitals for examination to ensure the accuracy of the laboratory results.