Thyroid function tests include serum free triiodothyronine, serum free thyroxine, and thyroid stimulating hormone. Serum free triiodothyronine is the most sensitive indicator for the diagnosis of hyperthyroidism and has a high application in the diagnosis of hyperthyroidism and hypothyroidism. Serum free thyroxine directly reflects the status of the thyroid gland and does not correlate with the concentration of thyroxine-binding globulin in the blood. Abnormalities in thyrotropin, the hormone that influences the secretion of the pituitary gland to promote the growth and function of the thyroid gland, can also reflect thyroid function.