Serum free prolactin concentrations in patients with systemic lupus erythematosus are associated with lupus activity.

OBJECTIVE: To determine in patients with systemic lupus erythematosus (SLE) the relationships among serum total and free prolactin (PRL) levels, isoforms of PRL and lupus activity.
METHODS: In a cross-sectional study, 259 patients with SLE were tested for serum total PRL, serum free PRL, and PRL in fractions obtained after gel filtration chromatography (in 70 sera taken at random) by immunoradiometric assay based on disease activity.
RESULTS: A significant correlation between direct PRL and free PRL levels was found in patients with and without lupus activity (r = 0.475, P<0.001); however, this was less so for non-active patients than for active patients (r=0.433, P<0.001 and r=0.909, P<0.001, respectively). SLE Disease Activity Index (SLEDAI) scores correlated positively with serum free PRL levels (r=0.314, P<0.001) and percentage of little PRL (r=0.33, P=0.005) and negatively with percentage of big big PRL (r=-0.3, P=0.012). Patients with active disease had higher serum free PRL levels (median 12.6 vs 9.3 ng/ml, P<0.001), higher percentages of little PRL (83.1 +/- 21.2 vs 63.6 +/- 24.8%, P=0.011) and lower percentages of big big PRL (9.4 +/- 18.0 vs 25.2 +/- 24.3%, P=0.031). Different clinical manifestations and serological parameters of lupus disease activity were more frequent in patients with free hyperprolactinaemia than in patients with normal serum free PRL levels (such as neurological manifestations, renal involvement, serositis, haematological manifestations, anti-double-stranded DNA and hypocomplementaemia; P<0.021).
CONCLUSION: An increase in serum free PRL levels, higher percentages of little PRL and lower percentages of big big PRL proved to be factors related to lupus activity in a subset of patients with SLE. These novel data must be taken into account in future studies aiming to establish a relationship between PRL and disease activity in SLE.