A TSH blood test is a medical test that measures the amount of thyroid-stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland and prompts the thyroid gland to produce and release its own hormones, thyroxine (T4) and triiodothyronine (T3), which are essential for maintaining your bodys metabolic rate. A TSH test is used to find out how well your thyroid is working and can tell if you have hyperthyroidism (too much thyroid hormone) or hypothyroidism (too little thyroid hormone) in your blood. The test can also detect a thyroid disorder before you have any symptoms. A TSH test is usually the first test doctors order when they suspect you have a thyroid disorder. The test involves simply drawing some blood from your body, and no preparation is needed. If you are being treated for a thyroid disorder, your TSH level will likely be kept between 0.5 and 4.0 µU/mL.