A TSH blood test measures the level of thyroid-stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland in your brain and regulates how much thyroid hormone your thyroid gland produces

. The thyroid is a small gland in the neck that produces hormones controlling your body's metabolism, heart rate, digestion, mood, and energy use. If thyroid hormone levels are too low, the pituitary gland produces more TSH to stimulate the thyroid to work harder. If thyroid hormone levels are too high, the pituitary produces less or no TSH

. The TSH test is used to evaluate thyroid function and can help diagnose:

• Hypothyroidism (underactive thyroid), indicated by a high TSH level
• Hyperthyroidism (overactive thyroid), indicated by a low TSH level

The test involves a simple blood draw, usually from a vein in the arm, with no special preparation needed

. It is often the first test ordered when thyroid problems are suspected or to monitor thyroid hormone replacement therapy

. In summary, the TSH blood test is a key diagnostic tool to assess whether your thyroid gland is functioning properly by measuring the hormone that controls thyroid activity