Macroprolactinemia in a patient with infertility and hyperprolactinemia

A significant number of patients with hyperprolactinemia have macroprolactinemia, a condition characterized by the preponderance of big-big prolactin with normal levels of free prolactin. As macroprolactin does not have biologic activity, such patients do not require further investigations or treatment for hyperprolactinemia. The case of a patient with hyperprolactinemia diagnosed during investigation of secondary infertility is presented. She was treated for over 2 years with dopamine agonists, with which her prolactin level normalized, but she remained infertile. Subsequent investigations demonstrated that she suffered from macroprolactinemia, not true hyperprolactinemia. The patient is currently not on dopamine agonist therapy, and although her total prolactin levels remain significantly elevated, her free prolactin levels have been in the normal range. Physicians should familiarize themselves with this entity and consider testing for it in patients with hyperprolactinemia to avoid an inappropriate diagnosis and unnecessary treatment.