Diagnosis

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. Several studies have shown that prolactin two-site sandwich immunoassays are susceptible to interference from 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.