Diagnosis of Syphilis Serologic reaginic tests (rapid plasma reagin [RPR] or Venereal Disease Research Laboratory [VDRL]) for screening blood and diagnosing central nervous system infections Serologic treponemal tests (eg, fluorescent treponemal antibody absorption or microhemagglutination assay for antibodies to T pallidum) The US Preventive Services Task Force recommends that asymptomatic, nonpregnant adolescents and adults who are at increased risk for syphilis infection be screened for syphilis.