The common cause of low thyroid hormone in patients with normal free T3 and free T4 is subclinical hypothyroidism, which needs to be treated in conjunction with the patient’s blood lipid level and clinical symptoms. If the patient’s lipid level is abnormal, it is recommended to give thyroid hormone treatment under the guidance of a doctor. Subclinical hypothyroidism often has no obvious symptoms or signs, and may show the symptoms of hypothyroidism, such as fatigue, fear of cold, dry skin, lack of energy, etc. Laboratory tests may only have elevated serum TSH levels, with normal FT3 and FT4 levels. According to TSH level, subclinical hypothyroidism can be divided into two categories: the first category is mild subclinical hypothyroidism: TSH<10μIU/ml; the second category is severe subclinical hypothyroidism, TSH≥10μIU/ml. If the patient is accompanied by symptoms of hypothyroidism, positive TPOAb, dyslipidemia or atherosclerotic disease, thyroid hormone treatment should be given; if the patient is not accompanied by the above conditions, regular monitoring of TSH changes should be carried out under the guidance of the doctor. If free T3 and free T4 are normal but thyroid stimulating hormone is low, it is recommended to go to the hospital and consult the relevant doctor, and the doctor’s advice should prevail.