A 32 year old man present to your office with complaints of a lesio on his penis that developed 3 days ago. He denies any fever or chills or pain. On further questioning, he reports an unprotected sexual intercourse with a stranger that he met in a night club 2 weeks ago. Physical examination reveals a normal vitals and no lymhadenopathy. The genitilia examination reveals the following findings as depicted in the picture
Most appropriate next Step in confirming the Diagnosis :
A. VDRL
B. RPR
C. FTABS
D. Cultures
E. Dark field microscopy of the scraping
Archer USMLE Step 3 Blog 
e
e
e
E. Dark field microscopy of the scraping……. Primary syphilis
e
E
E
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c.ftab is confirmatory test for syphilis.
c. ftabs is the confirmatory test for syphilis. dark field microscopy is the most accurate test but it is rarely done.
E is the answer as FTABS and VDRL might be falsely neg in primary syphilis..,
Screening Tests (VDRL, RPR) will be falsely ⊖ in 1° syphilis.
IF case describes a painless genital ulcer → order darkfield microscopy for Dx of 1° syphilis.
and need 3x negative tests on different days to R/o syphilis
there is a false ⊖ rate of 25% for both the VDRL and RPR. In other words, these serologic tests need several weeks to become ⊕, and they are only 75% sensitive in 1° syphilis.
E