This is a great question, because STI testing methods can vary province to province and are determined by provincial health authorities.
Here in Manitoba there are a couple testing methods for syphilis: to swab a suspected syphilis sore or to run a blood test.
If a sore is present, the testing clinician can send a swab to a lab for testing. Syphilis sores may show up anywhere from 3 days to 3 months after an infection. If you can get the sore swabbed while it is present, those results swab will be considered reliable, regardless of how long it’s been since your exposure of concern (when you think you may have come in contact with syphilis.)
Not everyone experiences symptoms though, which is where a blood test would come in. If you don’t have a sore present, and are relying on results from a blood test, we recommend that you get screened 3 months after your exposure of concern. Syphilis can be detected as early as a couple of weeks by a blood test, but it’s only after 3 months that we can rely on a negative result being conclusive.
So you are free to go for testing 6 weeks after a possible exposure, but the clinician may recommend that you return for another screen at the 3 month mark. If you have a sore at any time, having a clinician asses or swab it may be helpful.
Untreated syphilis can have serious health effects. But once you get tested, you can get any treatment you may require to clear the infection and move on with your sex life. We’d recommend using safer sex tools like condoms and lube while waiting for your test results.