Prolactin (PRL) is a hormone synthesized in the pituitary gland, a small gland at the base of the brain. It is responsible for lactogenesis in women. Prolactin tests help investigate the causes of abnormal milk flow (galactorrhea) or other fluid from the nipples. The test is also used in the differential diagnosis of amenorrhea (absence of menstruation) and infertility in women or decreased libido and/or erectile dysfunction in men. High prolactin levels (hyperprolactinemia) are normal during pregnancy and breastfeeding.
Hyperprolactinemia can also be seen in the presence of pituitary gland tumours (prolactinoma), anorexia nervosa, hypothyroidism, kidney and liver diseases, polycystic ovary syndrome, etc. Very low levels of prolactin and other hormones can be associated with a pituitary gland impairment (hypopituitarism or panhypopituitarism).
Prolactin levels are sometimes high in individuals as a result of the stress of having their blood taken. This can be confirmed with three prolactin tests taken at 15-minute intervals. Stress-induced prolactin levels will decrease in samples 2 and 3. Rarely, an abnormally large form of prolactin (macroprolactin) can produce a false high result. The presence of macroprolactin generally has no clinical significance.