C4A and systemic lupus erythematosus: Therefore, laboratory assessment for complement proteins, such as C3, C4, C3a, C5a, C3d, C4d, C-reactive protein, and autoantibodies, such as anti-nuclear antibody (ANA), anti-dsDNA, antinucleosome, and anti-C1q, were used extensively to measure the disease activity and severity in SLE.