Prolactin is a hormone secreted by the pituitary gland. Prolactin helps maintain the immune system in men and women and helps women produce breast milk. The hormone also helps nerve cells develop. 

The prolactin test measures blood levels of the hormone. High levels are normal in pregnant and breastfeeding women, but in women who are not pregnant and in men, high levels may indicate a pituitary gland or hypothalamic tumor. When these levels are elevated, women may experience irregular menstrual cycles, and men may experience a decreased libido. Abnormal levels of prolactin in men and women may cause fertility problems, including infertility. 

Elevated levels of prolactin can interfere with ovulation in women, decrease libido in men and decrease fertility for both genders. High levels have also been linked to kidney, pituitary gland and lung tumors. A damaged pituitary gland usually cannot produce normal amounts of prolactin; therefore low levels may indicate a health problem that should be addressed.

Keeping prolactin blood levels within the normal range is an important part of overall health and well-being, but some prescription drugs, such as antidepressants, pain medications and diuretics, can affect these levels. Ordering a blood test will let you know if your levels are within range.