What It Is
Prolactin is a hormone produced by the pituitary gland, the pea-sized gland near
the base of the brain that controls metabolism, growth, and sexual development. Although
prolactin is produced in small amounts in both males and non-pregnant females, its
main role is to stimulate lactation (milk production) in females during pregnancy
and maintain milk supply during breastfeeding. A prolactin test measures the amount
of this hormone in the bloodstream.
In a woman who breastfeeds, the nursing baby's demand for milk actually controls
the mother's supply. When a baby sucks at the breast, the woman's pituitary gland
releases more prolactin into her blood, increasing her milk production. If a mother
doesn't breastfeed, her prolactin levels will return to normal shortly after giving
birth.
Sometimes, though, prolactin levels are elevated even if a woman isn't pregnant
or breastfeeding, or in a male. The most common cause is a prolactinoma, a usually
benign (not cancerous) prolactin-producing tumor of the pituitary gland.
Why It's Done
Doctors may order prolactin tests to help diagnose, or monitor treatment of, prolactinoma.
Symptoms of a prolactinoma include headaches, vision problems (if tumor growth is
causing pressure on an optic nerve), and galactorrhea (milk production outside pregnancy
or breastfeeding, or in a male).
The prolactin test also may be used as part of a work-up for irregular menstrual
periods, fertility problems, some types of thyroid or adrenal gland dysfunction, anorexia,
and polycystic ovarian syndrome.
All these conditions can be associated with altered prolactin levels. A number
of medications and drugs can also stimulate the pituitary gland to release more prolactin
into the blood.
Preparation
No special preparations are needed for this test. However, since prolactin levels
vary throughout the day and night — they're highest during sleep, just after
waking up, following strenuous exercise, and during periods of emotional stress —
your doctor may request that the test be performed at a certain time of day (often
a few hours after waking up). You also should be sure that the doctor knows about
any medications or drugs your child may be taking, since some may increase prolactin
levels in the blood.
It may help to have your child wear a T-shirt or short-sleeved shirt on the day
of the test to make things faster and easier for the technician who will be drawing
the blood.
