Prolactin, Total and Monomeric - For some patients the level of Prolactin measured by immunoassay may be inaccurate with respect to the level of monomeric, biologically active Prolactin. The Macroprolactin by PEG Precipitation test can help to identify if a patient sample has elevated Prolactin due to mostly inactive protein-bound Prolactin (Macroprolactin).