Macroprolactin and the Roche Elecsys Prolactin Assay: Characteristics of the Reaction and Detection by Precipitation with Polyethylene Glycol

Abstract
Prolactin occasionally is present in serum in a macromolecular complex. The most common form is macroprolactin, an antibody-antigen complex of prolactin (PRL) and immunoglobulin G with a molecular mass of 150–170 kDa ( 1)( 2)( 3)( 4). The PRL component remains reactive (to various degrees) in immunoassays for PRL ( 5)( 6)( 7), and macroprolactin is cleared more slowly than PRL from the circulation, leading to apparent hyperprolactinemia ( 8).