Endocrine Abstracts

Macroprolactin, a high molecular mass complex of prolactin and an IgG antibody is confined to the vasculature and exhibits limited bioactivity in vivo. Using a panel of sera obtained from 10 subjects whose hyperprolactinaemia was due entirely to macroprolactin this study aims to compare the level of detection of macroprolactin by 9 of the most commonly used prolactin immunoassays.

The study involved 24 clinical laboratories employing the following 9 analytical methods: Abbott Architect and AxSYM; Bayer ACS 180, Centaur and Immuno-1; Beckman Access; DPC Immulite 2000; Roche Elecsys and Wallac DELFIA. A minimum of 2 measurement were obtained for each immunoanalyser.

Prolactin levels for any given macroprolactinaemic serum varied considerably from one method to another. In all cases Elecsys users reported the highest serum prolactin levels (range 828-4,604mU/L). Somewhat lower values were reported by DELFIA users followed by users of the Architect, Immuno-1 and AxSYM. Users of the Immulite 2000 reported prolactin levels approximately 50% of those measured by the 'high' reading methods (range 393-1,837mU/L). The lowest prolactin levels were reported by ACS 180, Centaur and Access users. In all instances monomeric prolactin levels measured following gel filtration were considerably lower than those reported by any of the immunoanalysers prior to chromatography (range 126-599mU/L).

This study clearly demonstrates that all of the immunoassay systems examined detected macroprolactin but to varying degrees. Based on the widespread use of such assays there currently exists the potential for a significant degree of misdiagnosis if secondary screening of hyperprolactinaemic sera for the presence of macroprolactin is not incorporated into routine laboratory practice.