From the Research
A rapid plasma reagin (RPR) titer greater than or equal to 1:8 is typically considered positive for syphilis treatment. This threshold is used because lower titers may represent either very early infection, previously treated infection, or a false positive result. The RPR test measures antibodies to cardiolipin, which are produced during syphilis infection, and higher titers generally correlate with more active or recent infection 1.
Key Points to Consider
- The standard regimen for early syphilis (primary, secondary, or early latent syphilis of less than one year's duration) is a single intramuscular injection of benzathine penicillin G 2.4 million units.
- For late latent syphilis or syphilis of unknown duration, the recommended treatment is benzathine penicillin G 2.4 million units intramuscularly once weekly for three consecutive weeks.
- After successful treatment, RPR titers should decline over time, which is why follow-up testing is important to ensure treatment effectiveness.
- In the context of clinical symptoms consistent with syphilis or known exposure, even lower titers may warrant treatment.
Evidence Supporting the Recommendation
The most recent and highest quality study, published in 2018, found that an automated latex turbidimetric RPR assay is a good alternative to the manual test for the diagnosis of syphilis and evaluation of treatment response 1. This study also found that a 4-fold decrement in RPR titer is a feasible criterion for successful treatment.
Clinical Implications
In clinical practice, a RPR titer of 1:8 or greater should prompt treatment with penicillin, and follow-up testing should be performed to ensure treatment effectiveness. The automated RPR test is a rapid and reliable method for diagnosing syphilis and evaluating treatment response, and it can handle more specimens than the manual test without interpersonal variation in interpretation 1.