2.3 Statistical analysis
The differences between patient groups and/or healthy controls were evaluated using the nonparametric Mann-Whitney U test. The correlations between CXCL13 concentrations and parameters of disease activity were calculated with Spearman’s rank correlation. Receiver operator characteristic (ROC) curves showed optimal cut-off values for CXCL13 to differentiate between patients with active SLE and patients with inactive SLE and between SLE patients with high avidity of IgG ANAs and SLE patients with low-avidity IgG ANAs. The significance level was set to p < 0.05. Data are displayed as the median ± interquartile range (IQR) unless otherwise stated. All statistical analyses were performed using SPSS software (version 20.0; IBM Inc., New York, USA).