Correlation of Serum Anti-C1q Antibody with Histological Characteristics in Lupus Nephritis

Background: Lupus nephritis (LN) is a major determinant of morbidity and mortality in systemic lupus erythematosus (SLE), with renal biopsy serving as the gold standard for evaluating disease activity and chronicity. However, its invasive nature underscores the need for reliable non-invasive biomarkers. Among them, serum anti-C1q antibodies have been implicated in LN pathogenesis, yet their association with histological parameters remains incompletely defined. Objective: This study aimed to investigate the correlation between serum anti-C1q antibody levels and histological characteristics in patients with lupus nephritis. Methods: A cross-sectional study was conducted at Dhaka Medical College and Hospital between March 2022 and August 2023, enrolling 55 patients with biopsy-proven LN. Serum anti-C1q antibody levels were measured by ELISA, and renal biopsies were classified according to the ISN/RPS 2004 criteria. Histological activity and chronicity indices were assessed, and correlations between antibody levels and histopathological features were analyzed using Spearman’s rank correlation. Results: The mean age of participants was 28.8 ± 9.03 years, with a female predominance (87.3%). Class IV LN was the most frequent subtype (34.5%), followed by class III (27.3%). Serum anti-C1q antibody levels were highest in proliferative classes (IV: 77.26 U/ml; III: 65.2 U/ml). Significant positive correlations were observed between anti-C1q levels and endocapillary hypercellularity (r=0.573, p=0.001), cellular crescents (r=0.632, p=0.001), interstitial infiltrates (r=0.450, p=0.001), and activity index score (r=0.765, p=0.001). No significant correlations were found with chronicity indices, including sclerosis, interstitial fibrosis, and tubular atrophy. Conclusion: Serum anti-C1q antibody levels strongly correlate with histological activity but not chronicity in lupus nephritis, particularly in proliferative classes. These findings suggest that anti-C1q may serve as a useful