C4A and systemic lupus erythematosus: Disease activity: MiRNA-200a negatively correlates with SLEDAI (r = -0.425), ESR (r = -0.284), CRP (r = -0.338), BUN (r = -0.263) and Scr (r = -0.345), while it positively correlates with C3 (r = 0.631), C4 (r = 0.524) and ALB (r = 0.394).Diagnostic for SLE: AUC 0.8379 (cut-off value = 2.225, sensitivity = 70%, specificity = 70%).Diagnostic for LN: AUC 0.7619 (cut-off value = 2.005, sensitivity = 80%, specificity = 76%)