C4A and systemic lupus erythematosus: The levels of antinuclear antibody were similar between active disease group and quiescent disease group, but SLE disease activity indexes (SLEDAI) (P < 0.0001) and levels of C3 (P < 0.0001), C4 (P < 0.0001), and anti-dsDNA (P < 0.0001) were significantly higher in active disease group than in quiescent disease group.