Raised serum prolactin in rheumatoid arthritis: Genuine or laboratory artefact?

Abstract

Objectives. Serum prolactin concentrations have been reported as higher, similar or tower in patients with rheumatoid arthritis (RA) compared with control subjects. We investigated whether low biological activity macroprolactin (a prolactin antibody complex), which is detected variably in different prolactin immunoassays, could account for the discrepant total prolactin results reported in RA. Methods. We compared serum total prolactin and free protactin in 60 women with RA and 31 female controls. Results. No subject had hyperprolactinaemia or macroprolactinaemia. Serum concentrations of total and free (monomeric) protactin were higher (P < 0.05) in women with RA [mean (S.D.), 225.6 (104.6) and 201.6 (95.4) mU/l respectively] compared with controls [175.0 (68.5) and 154.0 (60.9) mU/l respectively]. Conclusions. We report higher serum free prolactin concentrations in women with RA compared with control subjects. This result indicates that the higher serum total prolactin levels in patients with RA are the consequence of increased free prolactin concentrations and are not due to macroprolactin. © British Society for Rheumatology 2004; all rights reserved.