A potential biomarker of disease activity in systemic lupus erythematosus, systemic immune-inflammation index.

Objective: Biomarkers using routine laboratory tests accurately presenting systemic lupus erythematosus (SLE) disease activity may have important practical values in clinical settings. The primary purpose of this study was to investigate neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and systemic immune-inflammation index (SII; neutrophil X platelet/lymphocyte) as potential biomarkers of disease activity in cases with SLE.

Methods: In this case-control observational study, cases with SLE and demographically similar healthy controls were included. For clinical evaluation demographic features, disease duration and drugs were recorded. SLE clinical disease activity was assessed with SLEDAI scores. For laboratory assessments; erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and C3-C4 levels and anti-dsDNA positivity were recorded. Based on the simultaneous complete blood count (CBC) of the participants NLR, PLR and SII were calculated. The correlation between clinical and laboratory data was analyzed.

Results: 68 cases with SLE (64 women, 8 men) and 69 controls (65 women, 4 men) were included in this investigation. The demographic features of the cases and controls were similar. ESR, CRP, NLR, PLR and SII scores were statistically higher in cases with SLE than controls (p<0.000). Statistically significant positive correlations between SLEDAI and NLR, PLR and SII scores were demonstrated (p=0.01, r=0.505; 0.414; 0.698, respectively). We determined a cut-off value of SII as 681,3 presenting 77% sensitivity and 76% specificity to discriminate no-mild disease activity and moderate-higher SLE disease activity status. The SII cut-off value was determined as 681,3 presenting 77% sensitivity and 76% specificity (p<0.000, and AUC=0.930).

Conclusion: CBC indices were shown to be higher in cases with SLE than healthy controls in our study. By presenting a strong correlation with disease activity and discriminating ability of disease status, SII might serve as a biomarker supporting clinical evaluation in SLE.