Welcome to our Forum.  congratulations on your sensible approach to your sexual health.  We certainly endorse the practice of both partners getting screened for STIs as they enter a new relationship and congratulate you for doing so.  Unfortunately however, sometimes our tests let us down which is what I suspect has happened to you.  This result is most likely a false positive result.  Had you acquired syphilis, both the RPR and the treponemal test would have been positive.  Let me elaborate a bit on the basis of my assessment:

1. Test results are entirely consistent with a false positive result.,  When persons have syphilis, both tests are typically positive and if one test is positive and the other is not yet, it is the treponemal test becomes positive first.

2.  Most false positive tests have low RPR values such as yours.

3.  Persons with autoimmune diseases (such as thyroiditis) have a somewhat increased risk for false positive RPR results.

4.  Epidemiologically, over 70% of recently acquired syphilis amongst U.S. adults occurs in men with other men as sexual partners.  Thus assuming your partner has not had sex with other men, he is very low risk for having syphilis and transmitted it to you.

Finally, I will add, false positive RPRs are funny things. In many persons they will be transient in nature, then going away.  In other persons they may be chronic.  As a person with an autoimmune process you are at somewhat increased risk for future false positives- just want to make you aware of this so there will be no confusion with future health care providers.

I hope this information is helpful.  If anything is unclear or there are further questions, please don't hesitate to use your up to two follow-ups for clarification.  EWH