Macroprolactin

This test is used to study the causes of high levels of prolactin in the blood.

Prolactin is a hormone produced by the pituitary gland (hypophysis), a small gland located at the base of the brain. Its main role is to trigger and maintain the production of breast milk. Prolactin levels are useful when investigating infertility problems in men and women, and hypogonadism in men (low testosterone production by the testicles). Apart from pregnancy and nursing, the most frequent cause of high prolactin levels in the blood (hyperprolactinemia) is an adenoma (benign tumour) of the pituitary gland. Macroprolactin is an abnormally large prolactin molecule. It is produced when several prolactin molecules join together or when prolactin binds to an antibody. Its special shape prevents prolactin from being eliminated normally, resulting in an increase in measurable levels in the blood. Macroprolactin is usually inactive and thus constitutes a “false” positive result that the doctor will try to rule out before investigating further.