Abnormal prolactin levels can be either too high or too low, although they are more commonly too high. The scale for this test varies depending on the laboratory, but an abnormal levels of prolactin for a male are typically less than 2 nanograms per milliliter (ng/ml) of blood or more than 18 ng/mL. For a non-pregnant, non-nursing female, abnormal levels typically are less than 2 ng/ml or more than 29 ng/ml. Abnormal levels for a pregnant woman generally are less than 10 ng/ml or more than 209 ng/ml. This is usually the same for lactating women, but after about a week, postpartum the levels begin to decrease, and they continue to decrease throughout lactation the less a baby nurses.
Prolactin is the hormone that is produced by the pituitary gland and is responsible for lactation. Even men, non-pregnant and non-nursing women produce this protein hormone, although the reason is unknown. Prolactin is also known as the luteotropic hormone. An abnormal prolactin level can cause a variety of symptoms, including infertility. Other symptoms of an abnormal levels of prolactin include lactation not induced by postpartum, low sex drive, erectile dysfunction and amenorrhea.
Though the symptoms of an abnormal prolactin level can interfere with aspects of life such as conceiving a child, the cause of an elevated prolactin level is sometimes quite serious. For example, an extremely high level of the luteotropic hormone — more than 200 ng/ml — can be a result of a prolactinoma, a tumor located in the pituitary gland. Other conditions that cause a high level of prolactin include idiopathic hyperprolactinemia, hypothyroidism, kidney disease, nerve damage and cirrhosis. Certain medications, especially certain antipsychotics, also can cause an abnormal prolactin level.
A rise in prolactin might mean that a woman has ovarian cancer. After an elevated level of prolactin is detected, the next test done is a magnetic resonance imaging (MRI) test, which can detect whether there is a tumor present in the pituitary gland. If there's not a tumor, conducting further testing is the next step.
In some instances, a prolactin deficiency occurs. This condition usually is secondary to an anterior pituitary dysfunction. Postpartum pituitary necrosis or Sheehan syndrome accounts for a majority of prolactin deficiency cases. Other causes of a prolactin deficiency might include an anterior pituitary impairment, parasellar disease, hemochromatosis, sarcoidosis and tuberculosis.