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).