There are many indicators of thyroid function on the test list, what is the significance of each indicator? I will introduce them separately: total thyroid hormone (TT4); total triiodothyronine (TT3); free thyroxine (FT4); free triiodothyronine (FT3); thyrotropin receptor antibody (TRAb); thyroid peroxidase antibody (TPOAb); thyroglobulin antibody (TGAb). TT4, TT3, FT4 and FT3 are the most visual indicators of thyroid function. If they are significantly elevated, they may cause various symptoms of hyperthyroidism, and if they are significantly decreased, they may show symptoms of hypothyroidism. TT4 and TT3 are high in blood, but are affected by various factors: for example, TT4 and TT3 will increase in the presence of viral hepatitis, elevated estrogen, and pregnancy, while TT4 and TT3 will decrease in the presence of elevated androgens, long-term glucocorticoid use, and low albumin. Therefore, TT4 and TT3 should not be checked in these cases. FT3 and FT4 are less abundant in the blood and are more demanding to detect and prone to error, but they will not be affected by various factors as TT4 and TT3 are, so in many cases we will check FT4 and FT3 (e.g. pregnant women). Changes in TSH are usually secondary to TT4, TT3, FT4, FT, and in the opposite direction of their changes. In hyperthyroidism, TT4, TT3, FT4, FT3 are elevated and TSH will be decreased, while in hypothyroidism, TSH will be elevated. TRAb is the cause of Graves’ disease (one of the most common conditions of hyperthyroidism), so when TRAb is positive, the nail function generally shows hyperthyroid changes, at which point Graves’ disease can be diagnosed and treatment (medication, iodine 131 therapy, surgery) is required. When hyperthyroidism is present but TRAb is normal, one should be alert to the presence of other factors causing changes in nail function (e.g., non-Graves’ disease, which may not require treatment in some cases). The specificity of TPOAb and TGAb is low, which means that when these two indicators are elevated, especially when they are not significantly elevated, they have limited diagnostic value for the disease (a mild elevation may represent nothing more than thyroid destruction), but when TPOAb is significantly elevated (above 300 IU/ml), the possible presence of Hashimoto’s thyroiditis is generally considered (if Hashimoto’s thyroiditis is present but the thyroid function is normal, no medication is needed However, when TPOAb is significantly elevated (above 300 IU/ml), it is generally considered that Hashimoto’s thyroiditis may be present (if Hashimoto’s thyroiditis is present but the thyroid function is normal, no medication is needed), while TGAb is less specific and only elevated TGAb is of little diagnostic significance.