The triple A includes T3, T4 and TSH. The triple A is the simplest indicator to determine the function of the thyroid gland and is also an important indicator to diagnose hyperthyroidism and hypothyroidism. The triple test is mainly used in the following cases: a. Diagnosis of hyperthyroidism, according to the cause of hyperthyroidism, there are pituitary hyperthyroidism and thyroid hyperthyroidism, pituitary hyperthyroidism mainly manifests as elevated TSH and elevated T3 and T4, while thyroid hyperthyroidism mainly manifests as reduced TSH and elevated T3 and T4. Second, the diagnosis of hypothyroidism, according to the cause of hypothyroidism, can be divided into pituitary hypothyroidism and thyroid gland hypothyroidism, pituitary hypothyroidism is mainly manifested as TSH decreased, T3, T4 decreased, thyroid gland hypothyroidism is also known as primary hypothyroidism, mainly manifested as TSH elevated, T3, T4 decreased. Third, to diagnose subclinical hypothyroidism, if the T3 and T4 are normal and only TSH is elevated in the triple A gene, it is subclinical hypothyroidism. Therefore, the determination of thyroid function needs to be combined with T3, T4 and TSH for a comprehensive judgment.