Thyroid stimulating hormone is a very sensitive indicator of thyroid function, with a normal range of 0.27-4.2 mU/L. If you have hyperthyroidism, the standard for TSH should be less than 0.27 mU/L, and many patients with hyperthyroidism may have a lower level of less than 0.01 mU/L. In addition to the TSH value, the diagnosis of hyperthyroidism also depends on the level of free thyroid hormone . The diagnosis of primary hyperthyroidism is made if the free thyroid hormone level is also significantly higher than normal, accompanied by a decrease in thyroid stimulating hormone levels. If the TSH level alone is decreased and the free thyroid hormone level is normal, only subclinical hyperthyroidism can be diagnosed. Patients with subclinical hyperthyroidism generally do not require treatment. Patients with clinical-phase hyperthyroidism require oral anti-hyperthyroid medication.