The difference between thyroid ultrasound and A-5 is as follows: First, the examination methods are different: thyroid ultrasound examines the thyroid gland through ultrasound, while A-5 examines the thyroid gland by drawing venous blood. Ultrasound is mainly used to determine the size of the thyroid gland, the presence of nodules, the presence of enlarged lymph nodes and the echogenicity and blood flow of the thyroid gland, while the five thyroid tests in most hospitals should include T3, T4, TSH, TPOAb and TGAb. The clinical application is different. The thyroid ultrasound is mainly used to determine the shape and size of the thyroid gland, while the five items of thyroid function are mainly used to determine the functional status of the thyroid gland, such as detecting hyperthyroidism and hypothyroidism.