TSH stands for thyroid stimulating hormone. A TSH test is a blood test that measures this hormone. TSH levels that are too high or too low may be a sign of a thyroid problem.
The thyroid is a small, butterfly-shaped gland in the front of your neck. Your thyroid makes hormones that control how your body uses energy. Thyroid hormones affect nearly every organ in your body, including your heart. They help control your weight, body temperature, muscle strength, and even your mood. If you don't have enough thyroid hormones in your blood, many of your body functions slow down. If you have too much, many body functions speed up.
Your thyroid is controlled by a gland in your brain, called the pituitary gland. The pituitary gland makes thyroid stimulating hormone (TSH). TSH tells your thyroid how much thyroid hormone it needs to make.
If the thyroid hormone levels in your blood are too low, your pituitary gland makes larger amounts of TSH to tell your thyroid to work harder. If your thyroid hormone levels are too high, the pituitary gland makes little or no TSH. By measuring TSH levels in your blood, you can find out if your thyroid is making the right level of hormones.
A TSH test is used to find out how well your thyroid is working. It can tell if you have hyperthyroidism (too much thyroid hormone) or hypothyroidism (too little thyroid hormone) in your blood. But a TSH test can't show what is causing a thyroid problem.
If you take prescription thyroid hormone medicine because of hypothyroidism or because you had your thyroid removed, you'll have regular TSH tests to check your thyroid hormone levels. TSH tests are also used to monitor your thyroid hormone levels after treatment for hyperthyroidism.