Reporting of Post–PEG Prolactin Concentrations: Time to Change

Prolactin is the hormone most commonly measured in patients evaluated for reproductive disorders. The biologically active form of prolactin is the 23-kDa monomeric polypeptide secreted by the pituitary gland; however, circulating prolactin exists in a number of additional forms. Big prolactin (60 kDa) and macroprolactin (150 kDa), which are present in serum in varying quantities, can cause apparent hyperprolactinemia, but they have no clinical importance because they exhibit little biological activity. Despite efforts to improve assay specificity, all prolactin immunoassays in routine use detect both big prolactin and macroprolactin to varying degrees (1). The polyethylene glycol (PEG) precipitation test is widely used to detect pseudohyperprolactinemia caused by big prolactin and/or macroprolactin. Current best practice recommends that all sera with increased total prolactin concentrations be subfractionated by PEG precipitation to measure the bioactive monomeric prolactin concentration, a more clinically meaningful variable (2)(3). Subfractionation with PEG allows laboratories to distinguish patients with true hyperprolactinemia, in which there are supraphysiological concentrations of bioactive monomeric prolactin, from those with macroprolactinemia, which is characterized by increased concentrations of macroprolactin and/or big prolactin together with normal concentrations of bioactive monomeric prolactin. In the absence of PEG screening, misdiagnosis and consequent …