A prolactin test measures the level of the hormone prolactin, which is made by the pituitary gland, in your blood. See an illustration of the pituitary gland.

Pregnant women have high levels of prolactin, which helps make breast milk. During pregnancy, prolactin levels increase by 10 to 20 times. After the baby is born, prolactin stays high if you are breast-feeding. In women who do not breast-feed, prolactin levels return to normal soon after they give birth. After months of breast-feeding, prolactin levels may also return to normal levels even if you still breast-feed.

The pituitary glands of men and nonpregnant women also make prolactin but it is not clear what it does in the body for these people.

Prolactin levels are different throughout the day. The highest levels occur during sleep and shortly after you wake up. Prolactin levels also get higher during times of physical or emotional stress.

Many medicines can cause prolactin levels to go up. Tumors of the pituitary gland can sometimes cause prolactin to be made. A damaged pituitary gland may not be able to make normal amounts of prolactin so levels will be lower.

Why It Is Done

A test for prolactin is done:

• To find the cause of abnormal nipple discharge, or if a woman is not having periods (amenorrhea) or if a woman is having a hard time becoming pregnant (infertile).
• In a man when a pituitary gland problem is suspected. Also, a prolactin test may be done to check levels if a man lacks sexual desire or if he has a hard time having an erection (erectile dysfunction). Prolactin levels may be checked when a man's testosterone levels are really low.
• To see whether a tumor in the pituitary gland (called a prolactinoma) is making large amounts of prolactin.

How To Prepare

Do not eat or drink for a certain number of hours as instructed by your health professional before having a prolactin test.

A blood prolactin test is usually done about 3 hours after you wake up, sometime between 8 a.m. and 10 a.m.

Emotional stress or strenuous exercise just before the test can raise prolactin levels. You may be asked to rest quietly for up to 30 minutes before having your blood drawn.

Stimulation of the nipples can raise prolactin levels. Avoid nipple stimulation for 24 hours prior to prolactin testing. A woman having abnormal nipple discharge should not do anything to cause more discharge before the test.

How It Is Done

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Hook a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then a bandage.