C3 and Respiratory tract infection: In this hypothesis-generating analysis, respiratory tract infection (OR 1.43; 95% CI 1.19–9.9; p = 0.04), proliferative lupus nephritis (OR 2.12; 95% CI 1.32–17.34; p = 0.03), and hypocomplementemia (C3 < 90 mg/dL; OR 1.72; 95% CI 1.25–10.4; p = 0.02) suggested increased odds of mortality (Table 7).