Detection of Macroprolactinemia and Molecular Characterization of Prolactin Isoforms in Blood Samples of Hyperprolactinemic Women

Prolactin (PRL) circulates in the blood in the form of monomeric prolactin, dimeric prolactin and macroprolactin. Macroprolactin is a common cause of hyperprolactinemia. The objective of this study was to assess the prevalence of macroprolactinemia in hyperprolactinemic women and to undertake the biochemical characterization of macroprolactin. A retrospective cross-sectional study was conducted on one hundred hyperprolactinemic patients. All the sera were subjected to polyethylene glycol (PEG) precipitation and were divided into true hyperprolactinemics (PRL recovery >60%), probable macroprolactinemics (PRL recovery between 40 and 60%) and macroprolactinemics (PRL recovery < 40%). The prevalence of macroprolactinemia was found to be 34%. Sera from each group were further analyzed for isoforms of prolactin by gel filtration chromatography (GFC). The clinical spectrum of presenting complaints in the hyperprolactinemic cohort included oligomenorrhea, galactorrhea and infertility, but the presentation did not differ between macroprolactinemic and truly hyperprolactinemic patients. GFC showed three major PRL isoforms, viz., 23.5 kDa (monomeric), 47 kDa (dimeric) and 150-174.6 kDa (PRL-IgG complexes) along with the medium and heavy weight aggregates of prolactin. The results of the study showed that macroprolactinemia is one of the causes of hyperprolactinemia with high prevalence. It is recommended that all hyperprolactinemic patients be screened for macroprolactinemia.