What Is a Blood Test?

By taking and testing a small sample of a person’s blood, doctors can check for many kinds of diseases and conditions. Blood tests help doctors check how the body’s organs are working and see if medical treatments are helpful.

To help your child get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test. If your child is anxious about it, work together on ways to stay calm.

What Is Prolactin?

Prolactin (pro-LAK-tin) is a hormone made by the pituitary gland. Its main job is to stimulate lactation (milk production) during pregnancy and maintain milk supply during breastfeeding.

Sometimes, though, prolactin levels rise even without pregnancy or breastfeeding. The most common cause is a prolactinoma, a usually benign (not cancerous) prolactin-producing tumor in the pituitary gland. Symptoms can include headaches, vision problems (if tumor growth puts pressure on an optic nerve), and galactorrhea (milk production not linked to pregnancy or breastfeeding).

Why Are Prolactin Tests Done?

A prolactin test measures the amount of this hormone in the bloodstream. Doctors may order the test to help diagnose or monitor treatment of prolactinoma. 

They also may order one as part of testing for conditions linked to changes in prolactin levels, such as irregular menstrual periods, fertility problems, some thyroid or adrenal gland problems, anorexia, and polycystic ovarian syndrome.

Some medicines and drugs can also stimulate the pituitary gland to release more prolactin into the blood.

Prolactin levels vary throughout the day and night — they're highest during sleep, just after waking up, following heavy exercise, and during periods of emotional stress. So the test might be done at a certain time of day (for instance, a few hours after your child wakes up). Tell the doctor about any medicines your child takes because some may increase prolactin levels.

What if I Have Questions?

If you have questions about the prolactin test or what the results of the test mean, talk to your doctor.