Raised serum prolactin in rheumatoid arthritis: genuine or laboratory artefact?
OBJECTIVE
Serum prolactin concentrations have been reported as higher, similar or lower 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 prolactin in 60 women with RA and 31 female controls.


RESULTS
No subject had hyperprolactinaemia or macroprolactinaemia. Serum concentrations of total and free (monomeric) prolactin 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.
Ram
S
S
Department of Clinical Chemistry, New Cross Hospital, Wolverhampton, West Midlands. WV10 0QP, UK.
Blumberg
D
D
Newton
P
P
Anderson
N R
NR
Gama
R
R
D001172:Arthritis, Rheumatoid / Q000097:blood*; D001799:Blood Sedimentation; D005260:Female; D006801:Humans; D008875:Middle Aged; D011388:Prolactin / Q000097:blood*
C060678:prolactin, polymeric; D011388:Prolactin