Persistent Idiopathic Prolactin Elevation Merits Macroprolactin Estimation: A Case Report and Review of Literature

The prevalence of hyperprolactinemia ranges from about 0.4% in an unselected adult population to as high as 9%–17% in women with reproductive disorders. It may cause infertility in about 11% of the oligospermic males. Rarely, the cause of persistently elevated prolactin remains obscure even after thorough work up. Macroprolactinemia is biologically inactive, high-molecular-weight form of prolactin resulting from its binding to immunoglobulin G, causing a decrease in its clearance. We report the case of a 35-year-old female, detected to have hyperprolactinemia on multiple tests, during routine work up for primary infertility. Secondary causes for the same were ruled out. A magnetic resonance imaging (MRI) of the brain excluded a prolactinoma. This prompted an estimation of prolactin levels after polyethylene glycol precipitation which showed a decrease to 5.58 ng/mL, with <40% recovery, confirming the presence of macroprolactin. Thus, persistently elevated prolactin levels in the background of negative neurological imaging necessitate the estimation of macroprolactin.