Causes of high thyrotropin include primary hypothyroidism with hypothyroidism in Hashimoto’s disease, exogenous thyrotropin-secreting tumors (e.g., lung, breast), and recovery from subacute thyroiditis. In addition, ingestion of lithium metal, potassium iodide, and thyrotropin-releasing hormone can also increase thyrotropin. Thyrotropin is secreted by the pituitary gland and plays a key role in the functional control of the hypothalamic-pituitary-thyroid axis. The normal range of thyrotropin is 0.35-5.5μIU/ml. Due to different testing methods and reagents, the reference indexes vary from hospital to hospital and need to be analyzed specifically. Patients found to have elevated levels of thyrotropin should consult a medical professional for diagnosis and treatment.