TSH, or thyroid stimulating hormone, is an indicator used to assess thyroid function and is usually combined with FT3 and FT4 levels to make a comprehensive determination. If TSH is high and FT3 and FT4 are both low, hypothyroidism may be present. If TSH is high but FT3 and FT4 are normal, the condition is usually subclinical hypothyroidism, referred to as subclinical hypothyroidism. Subclinical hypothyroidism usually has no specific symptoms or mild symptoms, while patients with hypothyroidism may often show symptoms of reduced metabolic rate and decreased sympathetic excitability, such as easy fatigue, coldness, less sweating, weight gain, and slowed movement. The main causes of subclinical hypothyroidism and hypothyroidism include autoimmune damage, thyroid destruction, iodine overdose, and application of anti-thyroid drugs. Whether or not subclinical hypothyroidism requires treatment requires professional judgment by endocrinologists, taking into account the patient’s symptoms, TPOAb, TGAb, and TSH elevation; while most patients with hypothyroidism require long-term treatment, using levothyroxine sodium tablets and thyroid tablets as prescribed by the doctor, regular review, monitoring of the condition, and timely medical consultation in case of abnormalities.