Summary: Prolactin (PRL) circulates in the blood in the form of monomeric prolactin, dimeric prolactin and macroprolactin. Macroprolactin is a common cause of hyper prolactinemia. The objective of this study was to assess the preva lence 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 sub jected to polyethylene glycol (PEG) pre cipitation and were divided into true hyperpro lacti nemics (PRL recovery >60%), probable macroprolactinemics (PRL recovery between 40 and 60%) and macroprolactinemics (PRL recovery < 40%). The prevalence of macroprolac tinemia 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 macro pro lactinemic and truly hyperprolactinemic patients. GFC showed three major PRL isoforms, viz., 23.5 kDa (mono meric), 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 hyper prolactinemia with high prevalence. It is recommended that all hyperprolactinemic patients be screened for macro pro lactinemia.Keywords: macroprolactin, pseudohyperprolactinemia, big-big prolactin, IgG-prolactin, hyperprolactinemia, macroprolactinemia Kratak sadr`aj: Prolaktin (PRL) cirkuli{e kroz krvotok u obliku monomernog prolaktina, dimernog prolaktina i makro prolaktina. Makroprolaktin ~esto izaziva hiperpro lakti nemiju. Cilj studije bio je da se utvrdi prevalenca makroprolaktinemije kod `ena sa hiperprolaktinemijom i da se izvr{i biohemijska karakterizacija makroprolaktina. Sprovedena je retrospektivna studija preseka koja je obuhvatila stotinu pacijenata sa hiperprolaktinemijom. Svi uzorci seruma podvrgnuti su precipitaciji polietilen-glikolom (PEG) i podeljeni na prave hiperprolaktinemi~ne (PRL >60%), verovatno makro prolaktinemi~ne (PRL izme|u 40 i 60%) i makropro lak tinemi~ne (PRL < 40%). Utvr|ena prevalenca makropro laktinemije bila je 34%. U uzorcima seruma svih grupa ispitivano je prisustvo izoformi prolaktina putem hromatografske filtracije gelom (GFC). Prijavljene klini~ke smetnje u skupini pacijenata sa hiperprolaktinemijom obuhvatile su oligo menoreju, galaktoreju i neplodnost, ali se prezentacije nisu razlikovale izme|u pacijenata sa makroprolaktinemijom i pravih hiperprolaktinemi~nih pacijenata. GFC je pokazala tri glavne izoforme PRL, naime 23,5 kDa (monomer), 47 kDa (dimer) i 150-174,6 kDa (kompleksi PRL-IgG) zajedno sa srednje i veoma te{kim agregatima prolaktina. Rezultati studije po kazali su da je makroprolaktinemija jedan od uzroka hiper prolaktinemije koji ima veliku prevalencu. Preporu~uje se obavljanje pregleda za makroprola...