Low thyroid stimulating hormone may be caused by pituitary hypothyroidism, hyperthyroidism due to non-thyroid stimulating hormone tumor. The normal range of thyroid stimulating hormone is 0.35~5.5μIU/ml. Due to different examination methods and reagents, the reference indexes of each hospital are different and need to be analyzed specifically. Thyrotropin is secreted by the pituitary gland and plays a key role in the functional control of the hypothalamic-pituitary-thyroid axis and is the most valuable physiological marker of thyroid hormone action. Thyrotropin-releasing hormone from the hypothalamus stimulates the pituitary to produce thyrotropin, which stimulates the synthesis and secretion of thyroid hormones. If low thyrotropin is detected, it is recommended to consult the endocrinology department of a hospital and be guided by a physician.