Prolactin

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.

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.

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.

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.

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

There is very little chance of a problem from having blood sample taken from a vein.

Risks of a blood test

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

A prolactin test measures the level of the hormone prolactin, which is made by the pituitary gland, in your blood. Prolactin levels are different throughout the day. The highest levels occur during sleep and shortly after you wake up.

Normal

Normal values may vary from lab to lab.

High values

• High levels of prolactin (usually higher than 200 ng/mL) may mean a pituitary gland tumor (prolactinoma) is present. The higher the prolactin level, the more likely a pituitary gland tumor is present. If a prolactin level is over 200 ng/mL, a magnetic resonance imaging (MRI) test may be done to confirm a pituitary tumor is present. A normal or low prolactin level does not always mean there is no pituitary tumor. An MRI test may be done if a pituitary tumor is suspected.
• High levels of prolactin may mean that the pituitary gland is making excess prolactin for unknown reasons (idiopathic hyperprolactinemia).
• Other conditions that can cause high prolactin levels include pregnancy, liver disease (cirrhosis), kidney disease, and hypothyroidism.

Many conditions can affect prolactin levels. Your health professional will talk with you about any abnormal results in relation to your symptoms and medical history.

Reasons you may not be able to have the test or why the results may not be helpful include:

• Having a lot of emotional stress or doing strenuous exercise before the test.
• Trouble sleeping. Prolactin levels are highest during sleep so if you do not sleep well, your levels may be lower than normal.
• Stimulating your nipples.
• Taking certain medicines, such as birth control pills, high blood pressure medicines, tricyclic antidepressants, or medicines for mental illness, such as phenothiazines.
• Using cocaine.
• Having a test with radioactive tracer a week before the prolactin test.

• Men and nonpregnant women normally have low levels of prolactin. The only known problem caused by a lack of prolactin is not being able to make milk after pregnancy. Therefore, even people who have an abnormally low level of prolactin are not treated for the condition.
• Men may have a prolactin test 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. For more information, see the medical test Testosterone.
• Treatment for a pituitary gland tumor that is making too much prolactin includes medicines (such as bromocryptine), removing the pituitary gland, or radiation therapy to the gland. The choice of treatment is based on the size of the tumor and the health and age of the person being treated.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.