: Macroprolactin and Prolactin, Serum or Plasma

: What Is Prolactin?

: Prolactin is a hormone produced mainly by the pituitary gland, a small gland at the base of the brain. It plays a key role in breast development and milk production. Levels are normally kept in a narrow range, and problems with the pituitary or certain medicines can raise them.

: What Is Macroprolactin?

: Macroprolactin is a form of prolactin that is attached to an antibody, making the combined molecule larger. Because it clears from the body more slowly, standard lab tests may report a high prolactin level even though the amount of active, free prolactin is normal. This is sometimes called macroprolactinemia.

: Why the Test Is Done

: Doctors order this test when a prolactin result is unexpectedly high but the person has no typical symptoms such as unusual milk production, missed periods, or breast enlargement in men. It helps avoid unnecessary worry and further testing when the elevation is due to macroprolactin.

: How the Test Is Performed

: A blood sample is drawn from a vein, usually in your arm, and sent to the laboratory. There, the sample is tested for total prolactin and then processed to separate out the macroprolactin component, allowing the lab to estimate how much of the total is macroprolactin.