C3 and systemic lupus erythematosus: Some studies have shown that low complement levels (C3 and C4) are often associated with many comorbidities of SLE.[4,5] Our study indicated that only C3 but not C4 was significantly correlated with dry eye syndrome in terms of KSen (P < 0.001), SPK (P < 0.001), and Schirmer (P = 0.014).