Synonyms:   24-hour Urine Free Cortisol Test, Free Cortisol Test, Hydrocortisone Test Why It Is Done • To find the cause of an abnormal nipple discharge, an absence of menstrual periods (amenorrhea), or infertility in a woman. • In a man when a pituitary gland problem is suspected. • Evaluate a man's lack of sexual desire or his inability to have an erection • To determine whether a tumor in the pituitary gland is producing large amounts of prolactin. Test Overview A prolactin test measures the level of the hormone prolactin, produced by the pituitary gland, in your blood. . Pregnant women have high levels of prolactin, which prepares their breasts to produce milk. During pregnancy, prolactin levels increase by 10 to 20 times. After the baby is born, prolactin maintains the mother's milk production (lactation). In women who do not breast-feed their babies, prolactin levels return to normal soon after they give birth. Breast-feeding initially increases the level of prolactin. However, after months of breast-feeding, prolactin levels may return to normal nonpregnant and non–breast-feeding levels. The pituitary glands of men and nonpregnant women also produce prolactin. Its function in these people is not clearly understood. Prolactin levels vary throughout the day. The highest levels occur during sleep and shortly after you wake up. Prolactin levels increase during times of physical or emotional stress and during sleep. How To Prepare Patient fasting preferred.  Usually done 3 hours after you awake.  Avoid nipple stimulation for 24 hours prior to prolactin testing. You may be asked to rest quietly for up to 30 minutes before having your blood drawn.