Prolactin

At a Glance

Why Get Tested?

To help investigate unexplained flow of breast milk (galactorrhea), abnormal nipple discharge, absence of menstrual periods, and/or infertility in women; in men, to help diagnose the cause of decreased libido and/or erectile dysfunction; to detect and monitor a pituitary tumor that produces prolactin (prolactinoma)

When To Get Tested?

When you have symptoms of elevated prolactin, such as vision problems and headaches; during a workup for infertility; for follow-up of macroprolactin; when a man has low testosterone; periodically to monitor for recurrence of a pituitary tumor

Sample Required?

A blood sample drawn from a vein

Test Preparation Needed?

None; however, the sample should be collected 3 to 4 hours after waking.

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What is being tested?

Prolactin is a hormone whose primary role is to promote breast milk production (lactation). It is normally elevated in women during pregnancy and just after childbirth. It is normally low in men and non-pregnant women. This test measures the amount of prolactin in the blood.

Prolactin is produced by the front portion (anterior) of the pituitary gland, a grape-sized organ found at the base of the brain. The brain chemical dopamine and hormone estrogen control prolactin production and release from the pituitary gland. During pregnancy, the hormones prolactin, estrogen, and progesterone stimulate breast development and milk production. Following childbirth, prolactin helps initiate and maintain the breast milk supply. If a woman does not breastfeed, her prolactin level soon drops back to pre-pregnancy levels. If she does nurse, suckling by the infant plays an important role in the release of prolactin. There is a feedback mechanism between how often the baby nurses and the amount of prolactin released by the pituitary as well as the amount of milk produced.

A common cause of an abnormally elevated prolactin level is a prolactinoma, a tumor of the pituitary gland that causes excess production of prolactin. Prolactinoma is the most common type of pituitary tumor and is usually benign. They develop more frequently in women but are also found in men. Symptoms can arise both from the unintended effects of excess prolactin, such as milk production in a woman who is not pregnant or nursing and, rarely, in a man (galactorrhea), as well as from the size and location of the tumor.

If the anterior pituitary gland and/or the tumor enlarge significantly, it can put pressure on the optic nerve, causing headaches and problems with vision. It can also interfere with the other hormones that the pituitary gland produces. In women, prolactinomas can cause infertility and irregularities in menstruation, while in men these tumors can cause a gradual loss in sexual function and libido. Left untreated, prolactinomas may eventually damage the surrounding tissues.

Common Questions

How is the test used?

Prolactin testing may be used, along with other hormone tests, to help:

Determine the cause of breast milk production not associated with pregnancy or breast-feeding (galactorrhea)
Diagnose the cause of infertility and erectile dysfunction in men
Diagnose the cause of menstrual irregularities and/or infertility in women
Detect and diagnose tumors that produce excess prolactin (prolactinomas), monitor their treatment, and detect recurrences
Evaluate anterior pituitary function or detect some other pituitary disorder

When is it ordered?

Prolactin testing may be ordered when:

A person has signs and symptoms of a prolactinoma, such as unexplained headaches, visual impairment, and/or unexplained breast nipple discharge
A woman is experiencing infertility or irregular menstrual periods
A man has symptoms such as decreased sex drive (libido), nipple discharge, or infertility or has a low testosterone level

When a person has a prolactinoma, prolactin levels may be ordered periodically to monitor tumor growth and its response to treatment. They may also be ordered at regular intervals to monitor for prolactinoma recurrence.

Prolactin levels may be ordered, along with other hormone levels such as growth hormone, when a healthcare practitioner suspects that a person has a pituitary disorder such as hypopituitarism.

When a person has a condition or is taking medications that may affect dopamine production, prolactin concentrations may sometimes be monitored.

What does the test result mean?

Men and non-pregnant women will normally have only small amounts of prolactin in their blood. Prolactin levels do, however, need to be evaluated based on the time of day that they are collected. The levels will vary over a 24-hour period, rising during sleep and peaking in the early morning. Ideally, a person’s blood sample should be drawn 3 to 4 hours after waking.

A high level of prolactin is normal during pregnancy and after childbirth while the mother is nursing.

A high level may also be seen with a few other conditions, such as:

Tumors that produce and release prolactin (prolactinomas)
The eating disorder anorexia nervosa
Diseases of the hypothalamus
Underactive thyroid (hypothyroidism)
Kidney disease
Liver disease
Polycystic ovary syndrome
Other pituitary diseases and tumors

Levels of prolactin that are below normal are not usually treated but may indicate a general decrease in pituitary hormones caused by a pituitary disorder such as hypopituitarism.

Is there anything else I should know?

Prolactinomas are often small. Along with prolactin levels, a healthcare practitioner may perform an MRI (magnetic resonance imaging) of the brain to locate and determine the size of the tumor as well as the size of the pituitary gland.

Elevated prolactin can be caused by certain medications.

What other tests may be done to evaluate an elevated prolactin?

Depending on the purpose of testing, other tests that may be done include:

Testosterone—levels will usually be low in a male when prolactin is high
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)—to help evaluate ovulation and fertility
An MRI of the brain—to show pituitary enlargement and help locate a tumor
An eye examination—to evaluate problems with vision

Elevated prolactin levels require further laboratory tests to ensure that the elevation is not due to macroprolactin (see below).

If I have an elevated prolactin, why is my healthcare practitioner testing my thyroid?

Increased levels of prolactin are often seen in people with hypothyroidism (although they do not cause it). If you have elevated prolactin, your healthcare practitioner will most likely test you for hypothyroidism.

How are pituitary tumors that produce prolactin (prolactinoma) treated?

These tumors may be treated with medications that act like dopamine (such as bromocriptine or cabergoline) to decrease prolactin production. Treatment can reduce prolactin levels and symptoms and restore fertility, but the medications may have to be taken for several months or years. Surgery is sometimes necessary if the tumors are large or not responding to treatment. This surgery is delicate and requires an experienced surgeon. Sometimes, despite medication and/or surgery, the tumor recurs.

What is macroprolactin?

A number of otherwise healthy people have elevated prolactin levels because some of the prolactin in their blood is “macroprolactin.” Macroprolactin is prolactin that is typically bound to a protein (immunoglobulin), is not active in the body, and does not indicate the presence of disease. If an elevated prolactin is found in asymptomatic patients, further laboratory tests may be performed to make sure that this is not due to macroprolactin.

Looking For Test Results?

Looking For Reference Ranges?

You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

View Sources

Sources Used in Current Review

Shenenberger, D. (2018 March 16, Updated). Hyperprolactinemia. Medscape Endocrinology. Available online at https://emedicine.medscape.com/article/121784-overview. Accessed on 9/08/18.

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Corenblum, B. (2018 April 17, Updated). Pituitary Disease and Pregnancy. Medscape Endocrinology. Available online at https://emedicine.medscape.com/article/127650-overview. Accessed on 9/08/18.

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Wisse, B. et. al. (2016 August 7, Updated). Prolactin blood test. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/003718.htm. Accessed on 9/08/18.

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Sources Used in Previous Reviews

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Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Merck. Anterior Pituitary Function. The Merck Manual of Diagnosis and Therapy [On-line information]. Available online at http://www.merck.com/pubs/mmanual/section2/chapter6/6c.htm.

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(2002 July 24, Updated). Prolactinoma – males. MedlinePlus Health Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000337.htm.

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Benson, C. (Updated 2013 March 6). Prolactin Deficiency. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/124526-overview#showall. Accessed October 2013.

Shenenberger, D. (Updated 2013 March 21). Hyperprolactinemia. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/121784-overview. Accessed October 2013.

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Bielak, K. and Popat, V. (Updated 2012 June 5). Amenorrhea. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/252928-overview. Accessed October 2013.

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