Background Recent studies have shown that Serum Free Light Chain (sFLC) levels correlate with Systemic Lupus Erythematosus (SLE) disease activity, a result not demonstrated for C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR). Due to the short half-life (2 -6h) of the circulating sFLC, they may be of advantage to identify changes of disease activity in comparison to other laboratory assays.
Objectives Objective: to evaluate the total sFLC (∑FLC = sFLC-κ + sFLC-λ) levels in SLE patients, and compare the polyclonal sFLC increases with specific disease activity markers.
Methods 79 SLE patients previously diagnosed that fulfilled at least 4 ACR criteria were studied, together with 23 control samples from unrelated patients without known rheumatologic disease. Serum protein electrophoresis was preformed to discard the presence of a monoclonal protein. Analyzed parameters: sFLC, total immunoglobulins, anti-double stranded DNA (anti-dsDNA) and anti-nuclear antibodies (ANAS), C-reactive protein (CRP), Creatinine (Cre), C3 and C4. Spearman correlations, Mann-Whitney and ANOVA analysis were done by GraphPad Prism software.
Results 79 SLE patients were studied. Because SLE patient’s frecuently have renal impairment that may lead to increased serum levels of sFLC, 4 patients with increased Cre were excluded from further analysis. Correlations were found between ∑FLC and Cre (r=0,2706, P=0,0181), C3 (r= -0,4070, P=0,0006) and C4 (r= -0,3179, P=0,0088).
dsDNA-negative, dsDNA-positive, ANAS-negative and ANAS-positive groups’ ∑FLC medians were significantly different from control median. More interestingly, the dsDNA–positive and –negative ∑FLC median were significantly different (P<0,001), while it was not significant between ANAS-positive and – negative groups (P=0,2766).
Conclusions The results observed indicate that the ∑sFLC may distinguish two groups within the dsDNA-positive patients. These results may suggest a potential activity marker that adds information to the patient’s disease activity. Having a short half-life in the serum, the sFLC determination may allow to observe activity changes in a more timely fashion. Further prospective studies in our lab will evaluate the value of a new “activity algorithm” based on the dsDNA, C3 and C4determinations together with sFLC, needed to confirm the value of sFLC in evaluating disease activity.
Disclosure of Interest None Declared