Situations where PCR can be helpful in evaluating a patient for syphilis:
(1) primary chancre prior to serologic response
(2) false positive serologic test
(3) neurosyphilis (performed on CSF)
(4) gumma
(5) detection of resistance genes
(6) blood from neonates with congenital syphilis
Testing on blood is negative in latent syphilis and relatively insensitive in secondary syphilis.
PCR can help to make the diagnosis when:
(1) a darkfield microscope is not available or no one knows how to use it
(2) a silver stain is not available
Disadvantages of PCR:
(1) It is relatively expensive.
(2) It can have false positives.
(3) It may be affected by inhibitors giving a false negative result.
