According to WebMD, normal levels of TSH, or thyroid-stimulating hormone, are between 0.4 and 4.2 microunits per milliliter for adults, between 0.7 and 6.4 for children and between 1 and 39 for newborns. Values outside this range may indicate a problem with the thyroid or pituitary gland.
WebMD further mentions that lower levels than normal may show hypothyroidism, which is an underactive thyroid, and they may indicate a pituitary gland tumor in rare cases. Higher values than normal may be indicative of hyperthyroidism, which is a hyperactive thyroid gland, or they may indicate pituitary gland damage or a first-trimester pregnancy.
Other conditions that cause overactive thyroid are Graves disease, too much iodine, toxic nodular goiter and the use of certain medications. TSH levels may be kept low if a patient suffers from a pituitary condition or thyroid cancer.