At present, the most important indicators to reflect thyroid dysfunction in clinical practice are the three thyroid hormones, including thyroid stimulating hormone, FT3 and FT4, of which thyroid stimulating hormone is the most sensitive and earliest indicator of thyroid dysfunction. If a patient has subclinical hyperthyroidism or subclinical hypothyroidism, FT3 and FT4 may not have changed, but thyroid stimulating hormone levels have already changed. Therefore, thyroid stimulating hormone is the most important indicator of thyroid function. When patients undergo thyroid function tests, they should always check thyroid stimulating hormone as well as FT3 and FT4, as these three indicators can reflect the current state of thyroid dysfunction very accurately and completely.