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Prolactin (Blood)

Does this test have other names?

PRL test

What is this test?

This test measures the level of prolactin in your blood. Prolactin is a hormone made by the pituitary gland, which is in your brain. In women who are pregnant, prolactin stimulates the breasts to make breast milk.

If the prolactin-producing cells in your pituitary gland begin to mutate and grow out of control, they can form tumors called prolactinomas. Prolactinomas, also known as lactotroph adenomas, are usually not cancerous. They happen most often in women younger than 50. One symptom of a prolactinoma tumor is breast milk even if you're not pregnant. In men, prolactinomas may cause impotence or lower sex drive.

If you are diagnosed with a prolactinoma, your doctor may give you a medication called a dopamine agonist, such as bromocriptine or cabergoline. Cabergoline seems to be the more effective drug, and it has been shown to cut prolactin levels in roughly 90 percent of people with prolactinomas. Cabergoline also reduces the size of prolactinoma tumors.

Why do I need this test?

You may have this test if your doctor suspects that you have a prolactinoma tumor. Symptoms of this type of tumor include:

  • Flow of breast milk in a woman who's not pregnant or nursing

  • Breast tenderness in women

  • Enlarged breasts in men

  • Lower sex drive

  • Headache

  • Impotence in men

  • Vision changes

What other tests might I have along with this test?

Your doctor may also order an MRI scan of your brain to check for a prolactinoma.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given in micrograms per liter (µg/L). A normal blood level of prolactin is less than 20 µg/L. If your test result shows an abnormally high prolactin level, you may need imaging tests to find out whether you have a prolactinoma tumor.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Certain psychiatric medications, oral estrogen drugs, and hypothyroid medications may cause prolactin levels to be higher than normal. If you have kidney or liver disease, you may also have high prolactin levels.  

How do I get ready for this test?

You don't need to prepare for this test.