Thyroid Stimulating Hormone (TSH) 0.04 µIU/mL is low, and the reference range may vary from hospital to hospital.Low TSH indicates that it may be caused by hyperthyroidism, subclinical hyperthyroidism, pituitary pathology, and other disorders, as well as by medications. It should be combined with other tests such as thyroid hormone levels and imaging tests to clarify the diagnosis. The normal range of TSH is 0.35-5.5 µIU/mL, and the reference value may vary in different hospitals. 0.04 µIU/mL is generally on the low side, which can be seen in hyperthyroidism, subclinical hyperthyroidism, pituitary gland lesions, cortisolism, acromegaly and other diseases. The diagnosis should be made in conjunction with thyroid hormone levels and imaging studies. In addition, taking too much anti-thyroid drugs, such as methimazole, propoxythiazole, etc., may also cause low TSH. A visit to the hospital is recommended in the presence of thyrotropin 0.04 µIU/mL.