The Prolactin test measures a hormone produced by your pituitary gland that is primarily responsible for milk production. This test is a critical diagnostic tool if you are experiencing irregular periods, infertility, or unexplained milky discharge (galactorrhea). High levels when not pregnant can interfere with your body's normal reproductive signaling. This test is also the primary way to diagnose and monitor a benign pituitary tumor (prolactinoma). A simple blood draw is all it takes to find the hormonal root cause of your symptoms, putting you on the fast track to the right treatment.