Thyroid blood tests help figure out how well your thyroid gland is working. TSH helps the thyroid gland know when to make more thyroid hormones. Free T4 is the type of hormone that becomes active when ...

The thyroid-stimulating hormone (TSH) test measures the amount of TSH in the blood to convey how well a person’s thyroid functions. Normal levels are typically 0.4 to 4.0 milliunits per liter (mU/L) ...