Comparison of the cerebrospinal fluid (CSF) toluidine red unheated serum test and the CSF rapid plasma reagin test with the CSF venereal disease research laboratory test for diagnosis of neurosyphilis among HIV-negative syphilis patients in China.

In this study, we aimed to investigate the performance of nontreponemal antibody tests in cerebrospinal fluid (CSF) specimens from syphilis patients. From September 2009 to September 2012, CSF specimens were collected at the Shanghai Skin Disease Hospital in Shanghai, China, from 1,132 syphilis patients without HIV infection, including 154 with symptomatic and 56 with asymptomatic neurosyphilis. All of the CSF specimens underwent testing with a rapid plasma reagin (RPR) test, an RPR-V (commercial RPR antigen diluted 1:2 in 10% saline) test, the toluidine red unheated serum test (TRUST), and the Venereal Disease Research Laboratory (VDRL) test. Specificities, sensitivities, positive predictive values (PPVs), negative predictive values (NPVs), and kappa values were calculated to determine the performances of the tests. We compared results of the CSF-VDRL, CSF-RPR, CSF-RPR-V, and CSF-TRUST among patients with symptomatic and asymptomatic neurosyphilis who had reactive CSF-Treponema pallidum particle agglutination (TPPA) test results. Overall, the CSF-VDRL test was reactive in 261 patients (23.1%). There were no cases in which the CSF-VDRL was nonreactive and CSF-RPR, CSF-RPR-V, or CSF-TRUST was reactive. Agreement between the results of CSF-TRUST and CSF-RPR was almost perfect (κ=0.861), with substantial agreement between the results of CSF-RPR and CSF-RPR-V (κ=0.740). The sensitivities of CSF-VDRL, CSF-RPR, CSF-RPR-V, and CSF-TRUST were 81.4%, 76.2%, 79.5%, and 76.2%, respectively. Compared to CSF-VDRL, CSF-RPR, CSF-RPR-V, and CSF-TRUST had comparable PPVs and NPVs. However, the specificity of CSF-VDRL (90.3%) was significantly lower than those of the other tests (92.7 to 93.4%). Therefore, CSF-RPR, CSF-RPR-V, and CSF-TRUST can be considered alternative tests for neurosyphilis diagnosis in HIV-negative populations, particularly when the CSF-VDRL is not available.