Could systemic immune inflammation index be a new parameter for diagnosis and disease activity assessment in systemic lupus erythematosus?

Purpose Systemic immune inflammation index (SII) has been used as a marker of inflammatory status in various diseases, but its role in systemic lupus erythematosus (SLE) is unknown. We aimed to investigate the role of SII in SLE and its association with disease activity and renal involvement. Methods In this retrospective study, 76 patients with SLE were compared with 76 age- and gender-matched healthy control group in terms of SII, neutrophil-lymphocyte ratio (NLR), and platelet-lymphocyte ratio (PLR). SLE Disease Activity Index 2000 system (SLEDAI-2 K) was used to divide the SLE patients into an inactive group (SLEDAI-2 K < 9) and an active group (SLEDAI-2 K >= 9). Correlations between the ratios and both disease activity and renal involvement were analyzed. Results SLE patients had a higher level of SII compared with controls. The ability of SII in predicting SLE (AUC = 0.626) was lower than NLR (AUC = 0.723) and PLR (AUC = 0.666). SII was positively correlated with C-reactive protein (r = 0.288. p = 0.01), but no association between SII and SLEDAI-2 K scores was found. Significantly higher values of NLR, but not SII, were detected in patients with nephritis (p = 0.04). The best NLR cut-off value to predict SLE patients with nephritis was 2.32, with 78.5% sensitivity and 56.2% specificity. Conclusion For the first, we demonstrated that SII level was elevated in patients with SLE. However, NLR is a better marker than SII in predicting SLE and could serve as an indicator of nephritis. Larger-scale studies should be carried out to confirm our results.