At a Glance
Why Get Tested?
To determine whether your prolactin levels are higher (or occasionally, lower) than normal
When to Get Tested?
When you have symptoms of elevated prolactin, such as galactorrhea and/or visual disturbances and headaches; as part of a workup for female and male infertility; for follow-up of low testosterone in men; to monitor for recurrence of a prolactin-producing tumor
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None; however, the sample should be collected 3 to 4 hours after waking.
The Test Sample
What is being tested?
Prolactin is a hormone produced by the anterior portion of the pituitary gland, a grape-sized organ found at the base of the brain. Prolactin secretion is regulated and inhibited by the brain chemical dopamine. Normally present in low amounts in men and non-pregnant women, prolactin's primary role is to promote lactation (breast milk production).
Prolactin levels are usually high throughout pregnancy and just after childbirth. During pregnancy, the hormones prolactin, estrogen, and progesterone stimulate breast milk development. 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 secreted by the pituitary as well as the amount of milk produced.
Another common cause of elevated prolactin levels is a prolactinoma, a prolactin-producing tumor of the pituitary gland. Prolactinomas are the most common type of pituitary tumor and are usually benign. They develop more frequently in women but are also found in men. Problems resulting from them can arise both from the unintended effects of excess prolactin, such as milk production in the non-pregnant woman (and rarely, man) and 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 visual disturbances, and it can interfere with the other hormones that the pituitary gland produces. In women, prolactinomas can cause infertility and irregularities in menstruation; in men, these tumors can cause a gradual loss in sexual function and libido. If left untreated, prolactinomas may eventually damage the tissues around them.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed, but the sample is typically collected 3 to 4 hours after waking; fasting sample is preferred.
Ask a Laboratory Scientist
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Eckman, A. (Updated 2009 October 14). Prolactin. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003718.htm. Accessed April 2010.
Eckman, A. (Updated 2009 November 23). Prolactinoma. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000336.htm. Accessed April 2010.
(2009 May). Prolactinoma. National Endocrine and Metabolic Diseases Information Service [On-line information]. Available online at http://www.endocrine.niddk.nih.gov/pubs/prolact/prolact.htm through http://www.endocrine.niddk.nih.gov. Accessed April 2010.
Shenenberger, D. (Updated 2010 March 12). Hyperprolactinemia. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/121784-overview through http://emedicine.medscape.com. Accessed April 2010.
Mayo Clinic Staff (2010 March 6). Prolactinoma. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/prolactinoma/DS00532 through http://www.mayoclinic.com. Accessed April 2010.
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 767-768.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 354-355.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 900-901.
Fahie-Wilson, M (2003). In Hyperprolactinemia, Testing for Macroprolactin Is Essential, Clinical Chemistry. 2003;49:1434-1436. Available online at http://www.clinchem.org/cgi/content/full/49/9/1434 through http://www.clinchem.org. Accessed June 2010.
(May 2007) Fahie-Wilson M. Macroprolactin. Clinical Laboratory News Volume 33, Number 5. Available online at http://www.aacc.org/publications/cln/2007/may/Pages/series_0507.aspx through http://www.aacc.org. Accessed June 2010.
Suliman AM, Smith TP, Gibney J,McKenna T Joseph. Frequent Misdiagnosis and Mismanagement of Hyperprolactinemic Patients before the Introduction of Macroprolactin Screening: Application of a New Strict Laboratory Definition of Macroprolactinemia. Clin Chem 2003;49:1504-1509.
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 through http://www.merck.com.
(2002 February 17 Updated). Prolactin. MEDLINEplus Health Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003718.htm.
(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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