Subclinical hypothyroidism is the abbreviation of subclinical hypothyroidism. Patients with subclinical hypothyroidism usually lack obvious clinical signs and symptoms, and the diagnosis mainly relies on laboratory tests, which refers to the elevation of serum thyroid stimulating hormone levels only, with normal levels of total thyroxine and free thyroxine. According to the level of thyrotropin, subclinical hypothyroidism can be divided into two categories: mild subclinical hypothyroidism, TSH<10mIU/L; severe subclinical hypothyroidism, TSH ≥ 10mIU/L. Among them, mild subclinical hypothyroidism accounts for 90%. Patients with subclinical hypothyroidism should consult a professional doctor for diagnosis and treatment, and follow the doctor’s instructions for standardized treatment to avoid delays.