TestExplanationAdvantagesLimitations
Dark-field microscopyDirect visualization of spirochetes in ulcer exudate fluid

  • Immediate diagnosis

  • Allows for faster partner notification

  • Not useful for oral lesions (nonvenereal treponemes inhabit the mouth)

  • Dark-field microscope required

  • Requires experienced technician

Nontreponemal serology (Venereal Disease Research Laboratory test, rapid plasma reagin test)Detects antibodies to cardiolipin in blood

  • Inexpensive

  • Titers correlate with treatment success/failure

  • Lack reactivity in early primary syphilis

  • High titer levels may be read as false negative (prozone phenomenon)

  • 1 to 2 percent false-positive rate in pregnant women and in persons with autoimmune disorders, lymphoma, malaria, cirrhosis

Treponemal serology (fluorescent treponemal antibody absorption assay, Treponema pallidum particle agglutination test)Detects antibodies to T. pallidum in blood

  • Confirmatory test with high specificity and low false-positive rate

  • Becomes reactive earlier in primary syphilis than nontreponemal tests

  • Relatively expensive

  • Lack reactivity in early primary syphilis