Macroprolactin is the term used to describe complexed forms of the pituitary hormone prolactin which are found in blood. The most common complex found in blood consists of prolactin and immunoglobulin G (IgG). While the free prolactin hormone is active, prolactin in the macroprolactin complex does not have any biological activity in the body and is considered benign. However, macroprolactin is detected by all Laboratory tests that measure prolactin in blood. This leads to misdiagnosis of hyperprolactinaemia in many people, especially those with other symptoms, such as infertility or menstrual problems.