Calprotectin as a Biomarker of Disease Activity in Systemic Lupus Erythematosus Patients

Background: The chronic autoimmune illness known as systemic lupus erythematosus (SLE) has a wide range of clinical signs and fluctuating disease activity. One pro-inflammatory biomarker that has been suggested as a possible predictor of disease activity in autoimmune disorders is calprotectin. This study aimed to compare the level of serum and urine calprotectin in SLE patients versus control group, and to correlate the level of serum and urine calprotectin with clinical, laboratory radiological and ultrasonographic parameters of disease activity and severity. Methods: This case-control study included 92 participants, divided into three groups matched for age and sex, with no history of autoimmune or rheumatic diseases. Serum and urinary calprotectin levels were measured and correlated with the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI), laboratory markers, and systemic involvement. Results: Serum and urine calprotectin levels were significantly elevated in SLE patients compared to controls (P<0.001), with higher levels in active versus inactive cases (P< 0.05). Serum calprotectin showed strong positive correlations with SLEDAI (r=0.713), anti-dsDNA (r=0.653), ANA titer (r=0.656), ESR(r=0.494), CRP(r=0.442), serum creatinine (r=0.456), and urine protein (r=0.444), and negative correlations with complement C3(r=-0.461) and C4(r=-0.500). Urine calprotectin demonstrated similar trends. ROC analysis showed that serum calprotectin at a cutoff >2.8μg/mL had 96.77% sensitivity and 93.33% specificity (AUC=0.992), while urine calprotectin at >0.9μg/mL had 95.16% sensitivity and 73.33% specificity (AUC=0.986) for detecting disease activity. Conclusions: This study demonstrated that serum and urine calprotectin can serve as a non-invasive, accessible indicator for monitoring disease activity and guiding clinical assessment in SLE management.