Fig. 1

Plasma C4d levels are increased in patients with systemic lupus erythematosus (SLE) in the cross-sectional study, and C4d is convincing as an accurate marker for identifying higher disease activity (DA). a C4d levels in healthy control subjects (n = 77) and patients with SLE at lower (n = 98) and higher (n = 98) DA. Data are presented as medians with 25–75% quantiles plus whiskers, and significance was calculated using the Kruskal-Wallis rank-sum test. b Ratio of higher DA to lower DA of C4d, C3, and C4 levels in patients with SLE (n = 98). The dashed line indicates equal levels at higher and lower DA. Data are presented as medians with 25–75% quantiles plus whiskers. c Area under the ROC curve analysis shows that only C4d, but not C3 and C4, exhibits accuracy as a marker for higher DA. d Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for C4d, C3, and C4 as markers for higher DA. Data are presented with 95% CIs