TSH stands for thyroid stimulating hormone, which is a hormone released by the hypothalamus to stimulate the release of hormones from the thyroid gland. The TSH level refers to the amount of TSH found in the blood. A person's TSH level can be determined with a simple blood test.
Results of a TSH level blood test generally take two or three days to process. Healthy adults should have a TSH level between 0.4 and 4.2 microunits per milliliter of blood. Children should have a level between 0.7 and 6.4 microunits per milliliter, and newborns should have a level between 1 and 39 microunits per milliliter. Levels higher than the upper limit may indicate an underactive thyroid gland that's not responding to TSH or the presence of a pituitary tumor. Low TSH levels may indicate damage to the pituitary gland or an overactive thyroid gland that's over-responsive to TSH.
There are several reasons why a doctor may order a test to measure TSH levels. If a person is experiencing symptoms of an underactive thyroid gland, such as weight gain, tiredness and feeling cold all of the time, measuring the TSH level along with levels of thyroid hormones can tell a physician whether the thyroid gland is working properly. A person's TSH level can also indicate whether a prescribed thyroid replacement medication is working properly.