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 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
A blood sample drawn from a vein
None; however, the sample should be collected 3 to 4 hours after waking.
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.
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.
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.