What is a prolactin test?

A prolactin (PRL) test measures the level of prolactin in a sample of your blood. Prolactin is a hormone produced by the pituitary gland, a small gland at the base of the brain. Hormones are chemical messengers in your bloodstream that control the actions of certain cells or organs.

Prolactin affects many body processes. But its main role is to signal breast tissue to grow during pregnancy and make milk for breastfeeding after birth. So, prolactin levels in pregnant women and new mothers are normally high.

In nonpregnant women and men, prolactin levels are normally low.

Having higher-than-normal prolactin levels (hyperprolactinemia) can affect the body in different ways:

• In women, it can affect how the ovaries work and can cause menstrual problems and infertility.
• In men, it can affect how the testicles work and can cause a lower sex drive and erectile dysfunction (ED). Also known as impotence, ED is the inability to get or maintain an erection.
• In men and women who are not pregnant or breastfeeding, it can signal your body to start making breastmilk.

Higher-than-normal prolactin levels can have different causes:

• Prolactinoma, a benign (noncancerous) tumor growing on the pituitary gland. This is the most common cause. This type of tumor makes prolactin, which leads to higher-than-normal levels of prolactin in the blood.
• Certain medicines.
• Certain health conditions, such as hypothyroidism (underactive thyroid), kidney disease, and chest injuries
• Other pituitary gland tumors.

A prolactin test can't show the cause of higher-than-normal prolactin levels. But finding out what your levels are can help your health care provider decide which other tests you need to diagnose the cause of your symptoms.

Other names: PRL test, prolactin blood test

What is it used for?

A prolactin test is most often used with other tests to help:

• Diagnose a prolactinoma
• Find the cause of irregular menstrual periods
• Find the cause of infertility in men and women
• Find the cause of a man's low sex drive and/or erectile dysfunction
• Monitor a known prolactinoma to see if:
  • Treatment is working.
  • The tumor has come back after treatment.

Why do I need a prolactin test?

You may need a prolactin levels test if you are having symptoms that could be caused by higher-than-normal prolactin levels. The symptoms are different for women and men.

In women, symptoms may include:

• Changes in menstruation (irregular periods or absence of periods)
• Production of breast milk when not pregnant or breastfeeding
• Nipple discharge
• Infertility

Symptoms also depend on whether you have gone through menopause, which is when your periods stop, normally around age 50.

In men, symptoms may include:

• Nipple discharge
• Erectile dysfunction/impotence
• Enlarged breasts (gynecomastia)
• Decreased facial and body hair
• Low sex drive

If you have higher-than-normal levels of prolactin because of a prolactinoma, you may also have other symptoms. A prolactinoma that is not treated can grow large enough that it presses against nearby parts of the pituitary gland and the brain. This can cause:

• Headaches
• Changes in vision, if the tumor is pressing on the optic nerve (the nerve at the back of the eye)
• Low levels of other pituitary hormones, such as thyroid hormones and cortisol

If you've already been diagnosed with high prolactin levels from a prolactinoma, you may need prolactin testing to check whether your treatment is working. After treatment, you may be retested to see if the tumor has come back.

What happens during a prolactin test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Your provider will let you know if you need to do anything to prepare for your test. You may be asked to fast (not eat or drink) for several hours before your test.

Prolactin levels change throughout the day. For accuracy, your blood sample will usually be scheduled for three to four hours after you wake up.

Certain medicines and vitamins can affect prolactin levels. So, be sure to tell your provider about anything you are taking. But never stop taking any medicine without talking with your provider first.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

To understand what the results of your prolactin levels test mean, your provider will consider your symptoms, sex, and medical history, and the results of any other tests you had.

In general, for men and women who aren't pregnant or breastfeeding, higher-than-normal prolactin levels may be a sign of many types of conditions, such as:

• Prolactinoma or another pituitary disorder.
• A disease of the hypothalamus. The hypothalamus is an area of the brain that controls the pituitary gland and other body functions.
• Hypothyroidism.
• Cirrhosis (scarring of the liver).
• Kidney disease.
• Polycystic ovary syndrome (PCOS) in women.

If your results show high prolactin levels, your provider will usually order other blood tests to help diagnose the cause. If your provider thinks you may have a prolactinoma, you may also have an MRI (magnetic resonance imaging) scan to check your pituitary gland for tumors.

Treatment for high prolactin levels depends on the cause. Treatment is usually medicine. Surgery may be needed for certain pituitary tumors.

Higher-than-normal prolactin levels don't always mean you have a medical condition that needs treatment. Diets high in protein and certain medicines can cause high levels. Small increases in prolactin may be caused by stress, exercise, and even having sex. So, depending on your symptoms and medical history, your provider may suggest testing you again to see if your prolactin levels remain high.

Lower-than-normal prolactin levels are rare but may be a sign of a pituitary disorder. Without enough prolactin, a woman may not make enough milk to breastfeed after birth. This is usually the only symptom of abnormally low prolactin levels.

If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.