C1q and anti-C1q antibody levels are correlated with disease severity in Chinese pediatric systemic lupus erythematosus.

The aim of this study was to measure the level of serum complement lq(Clq) and anti-C1q antibodies (ClqAb) in pediatric systemic lupus erythematosus (PSLE), and then analyze the correlation between the levels of serum Clq and ClqAb with disease activity and kidney damage. We investigated 90 PSLE patients, including 43 patients in active stage and 47 patients in remission. Our results showed that the level of serum Clq of PSLE patients was significantly lower than the level of healthy children and children with other rheumatic diseases. In contrast, the level of ClqAb of PSLE patients was significantly higher than the other groups. The level of serum Clq was negatively correlated with systemic lupus erythematosus (SLE) disease active index (SLEDAI) and the level of ClqAb was positively correlated with SLEDAI and kidney damage. The sensitivity of using ClqAb levels to diagnose PSLE was 95.6% and the specificity was 97.5%. 93.0% SLE patients who had high C1qAb levels also showed kidney damage. Therefore, the levels of C1q and C1qAb in serum reflect the disease severity of SLE. Decreased Clq and increased C1qAb is closely correlated with lupus nephritis (LN) in children and may have diagnosis values for child LN.