Essential Thyroid Function (TSH) Test - Thyroid Stimulating Hormone (TSH) Test

This test measures the concentration of thyroid-stimulating hormone (TSH, or thyrotropin) in the blood. This hormone is secreted by the anterior pituitary gland in the brain, and its primary function is to stimulate the thyroid gland to produce and secrete its hormones (T4 and T3). TSH is a highly sensitive indicator of the inverse relationship between the pituitary and thyroid glands; it rises when thyroid hormones are deficient (hypothyroidism) and falls when they are overactive (hyperthyroidism), making it the best initial screening test.