In how many weeks syphilis is detectable by test?

2-4 weeks: There is a window period during which time you might not test positive for syphilis but still be infected. This window period can vary by type of test -- and probably from person to person. The syphilis lesion (chancre) usually appears 1-3 weeks after exposure and the vdrl/rpr blood test usually is reactive 1-2 weeks after the lesion appears.