[Macroprolactinemia. Risk of misdiagnosis and mismanagement in hyperprolactinemia].

Prolactin is found in serum in different molecular forms differing in molecular size, i.e., monomeric prolactin (molecular mass 23 kDa), "big prolactin" (50-60 kDa, possibly a dimer or a complex with receptor) and "big, big prolactin" or "macroprolactin" (150-170 kDa), usually a complex with immunoglobulin G. Macroprolactin, generally considered to be biologically inactive, accounts for the major part of prolactin immunoreactivity in some patients. The concentration may be unchanged for many years. Different immunoassays for prolactin differ in reactivity with this macromolecular complex. Awareness of macroprolactin as a potential source of misdiagnosis is clinically important. However, as witnessed by results from measurements of a sample distributed by EQUALIS in 2001, and also by a recent inquiry, only a small minority of Swedish laboratories are capable to establish the presence of macroprolactin. Through efforts done by UK NEQAS, an increasing number of British laboratories now have this capacity. Laboratories performing prolactin measurements should have access to methodology to establish macroprolactinaemia. They also have a duty to inform patients' physicians about these problems and how they are solved.