Diagnostic value of serum anti-C1q antibodies in patients with lupus nephritis: a meta-analysis

The autoantibodies against C1q (anti-C1q) have been reported in patients with systemic lupus erythematosus (SLE). In the past decade, though there were increasing studies suggesting it is relatively specific in lupus nephritis (LN), its overall diagnostic value in LN has not been evaluated. The meta-analysis was conducted to quantitatively evaluate the diagnostic accuracy of autoantibodies against C1q in patients with LN, and to provide more precise evidence of a correlation between anti-C1q antibodies and activity of LN. We searched Medline, Embase and Cochrane databases and contacted authors if necessary. A total of 25 studies including 2,502 patients with SLE and 1,317 with LN met our inclusion criteria for this meta-analysis. Among all 25 studies, 22 studies were available for comparison between SLE with and without LN, and 9 studies compared anti-C1q between patients with active and inactive LN. Summary receiver operating characteristic (SROC) curve was used to summarize comprehensive test performance. The QUADAS tool was used to assess the quality of the studies. For the diagnosis of LN, the pooled sensitivity and specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR) of anti-C1q were 0.58 (0.56-0.61, 95% confidence interval 95% CI]), 0.75 (0.72-0.77, 95% CI), 2.60 (2.06-3.28, 95% CI), 0.51 (0.41-0.63, 95% CI), and 6.08 (3.91-9.47, 95% CI) respectively. The area under the SROC curve (AUC) was 0.7941. For comparison between active and inactive LN, the weighted sensitivity, specificity, PLR, NLR and DOR were 0.74 (0.68-0.79, 95% CI), 0.77 (0.71-0.82, 95% CI), 2.91 (1.83-4.65, 95% CI), 0.33 (0.19-0.56, 95% CI), and 10.56 (4.56-24.46, 95% CI) respectively. The AUC was 0.8378. In conclusion, this meta-analysis indicates that anti-C1q antibodies have relatively fair sensitivity and specificity in the diagnosis of LN, suggesting that the presence of anti-C1q antibodies may be a valuable adjunct for predicting LN and assessing renal activity.