C3 and lupus nephritis: The authors found that complement split products C4d and Bb were more sensitive predictors of future moderate to severe disease activity than serum C3 and C4 (sensitivity 65 to 93% as compared to 53 to 64%), However, urinary C3d levels best correlated with kidney disease activity and were superior to all the plasma markers C3, C4d, Bb, C5b-9 and anti-dsDNA antibody levels in distinguishing patients with active lupus nephritis from those without (P-value =0.02) (49).