CXCL13 and neurosyphilis: The combination assay of the ratios of CSF/serum CXCL13, CXCL10 and CXCL8 (Model 2) had 90.4% and 86.8% sensitivity, 93.7% and 94.6% specificity, and yielded the AUCs of 0.966 and 0.938 (95% CI 0.945–0.986 and 0.896–0.981) for the diagnosis of all neurosyphilis and asymptomatic neurosyphilis, respectively (Tables 1 and 2).