C3 and systemic lupus erythematosus: This lack of association between HC and disease activity (flares) may reflect the fact that not all SLE manifestations are immune complex mediated (Table 2) and suggest that while C3 and C4 monitoring in general is probably not advantageous or cost-effective in SLE as a predictor of damage accrual, it may potentially be clinically useful in a selected group of patients where significant prior disease activity has occurred in the context of HC [9, 29, 33–35].