Serum and Urine S100A8 as a New Biomarker of Lupus Nephritis.

Lupus nephritis (LN) is a common manifestation of systemic lupus erythematosus (SLE) requiring reliable biomarkers for diagnosis and monitoring. This study set out to assess serum and urinary S100A8 as potential biomarkers for LN and investigate their correlation with traditional disease markers. This case-control research comprised 70 participants: 30 LN patients, 20 non-LN SLE patients, and 20 healthy controls. Disease activity was assessed using SLEDAI-2K scores. Serum and urinary S100A8 levels were measured using ELISA. Serum and urinary S100A8 levels were significantly higher in LN patients compared to both non-LN SLE patients and controls (p<0.001). Both markers showed positive correlations with ESR, UPCR, and SLEDAI-2K scores (p<0.05). Serum S100A8 demonstrated 70% sensitivity and 80% specificity at a cutoff >1340 pg/ml (AUC=0.835, p<0.001), while urinary S100A8 showed 83.33% sensitivity and 47.5% specificity at >904 pg/ml (AUC=0.827, p<0.001) for LN diagnosis. Serum and urinary S100A8 levels correlate significantly with LN disease activity and demonstrate promising diagnostic potential. These findings suggest S100A8 could serve as a valuable biomarker for LN diagnosis and monitoring, complementing existing disease markers.