A number of different factors can cause prolactin levels to rise or fall. Some of these are normal bodily functions, such as pregnancy, and some are caused by temporary conditions, such as stimulation of the breasts or exercise. In some cases, the use of certain medications or the presence of various medical conditions has been shown to raise prolactin in both men and women. Abnormally low levels of prolactin do not cause problems in patients who are not currently pregnant or breastfeeding.
In healthy adults, the prolactin level is affected by whether or not a woman is pregnant or breastfeeding. Though the pituitary gland of both men and women releases prolactin, levels in the blood are usually low — between 2 and 18 nanograms per milliliter (ng/mL) in men and 2 and 29 ng/mL in women. Women who are breastfeeding can have significantly higher levels, with normal levels between 10 and 209 ng/mL. In otherwise healthy women, stimulation of the breasts can temporarily increase prolactin levels, and in both healthy men and women, exercise or stress can increase the body's production of this hormone.
Certain medical problems also cause increased levels of prolactin in both men and women. The hormone is secreted by the pituitary gland in the brain, and a tumor that presses against this gland or that forms within the gland can cause it to secrete greater amounts of prolactin. Problems with the kidneys or the thyroid have also been known to increase prolactin.
Increased prolactin levels can also be caused by certain medications. Some H2 blockers, antidepressants, and medications containing estrogen can cause a rise in prolactin. Tranquilizers such as trifluoperazine can also have this effect. Medications that lower prolactin do not cause problems for patients who are not pregnant or breastfeeding because normal levels of prolactin are generally quite low.
A simple blood test can be performed to find out what a patient's prolactin levels are. Doctors will often test for prolactin more than once to see how the levels fluctuate over time. If prolactin levels are found to be high, other tests can be done to determine the reason. In some cases, high levels of prolactin can be indicative of a serious or even life-threatening condition.