Is Circulating Anti C1q Antibody a Better Predictor of Lupus Nephritis Activity Than Serum Levels of Anti-ds DNA Antibody and Complement Components 3 and 4?

Background Lupus nephritis (LN) can cause significant morbidity and mortality if not diagnosed and treated in time. This study aimed to assess a non-invasive biomarker (anti-C1q antibody) for predicting LN’s histopathological activity. Materials and Methods This single center observational study included 50 patients with newly diagnosed LN. Serum anti-C1q antibody, anti-dsDNA antibody, C3, and C4 levels were correlated with National Institute of Health (NIH) activity index on kidney biopsy and SELENA SLEDAI instrument score, using Spearman’s correlation coefficient. ROC curves were drawn for these biomarkers’ serum levels for predicting NIH activity index score >10 on kidney biopsy. Results The coefficients of correlation of anti-C1q antibody, anti-dsDNA antibody, C3, and C4 serum levels with LN histological activity were 0.5, 0.43, 0.48, and 0.3, respectively, and with SELENA SLEDAI score were 0.7, 0.45, 0.40, and 0.3, respectively. A 30 U/mL cut-off level for the anti-C1q antibody titer had a 61% sensitivity, 78% specificity, and 72% predictive accuracy in assessing histological LN severity with an activity index > 10 on kidney biopsy. Conclusion Anti-C1q antibody serum levels correlated better with LN activity than anti-ds DNA antibody, C3, and C4 serum levels. Anti-C1q antibody serum levels > 30 U/mL can be used to predict severe proliferative LN with an activity index > 10 on kidney biopsy.