Is RPR Test Reliability High for Syphilis Detection?

Is the accuracy of the RPR test high?

Hello Doctor, I would like to ask about the reliability of the RPR test results.
I had the RPR test done 80 and 90 days after engaging in high-risk behavior, and both results were non-reactive.
Does this mean that I do not have a syphilis infection? If I want to retest, should I do it in the third week after 90 days or in the third month after 90 days? Thank you for your response.

Eag, 30~39 year old female. Ask Date: 2020/11/30

Dr. Cai Zhuorong reply Urology

1.
Is the reliability of the RPR test high? According to the literature, the sensitivity of RPR is 86% and the specificity is 98%.

2.
If the results are all non-reactive, does that mean there is no syphilis infection? If we exclude the possibility of false negatives, then yes, it does indicate no infection.
3.
If a retest is desired, according to the CDC guidelines, a different type of test should be performed rather than repeating the same test.
If the nontreponemal test is negative, the laboratory should perform a different treponemal test (preferably one based on different antigens than the original test) to confirm the results of the initial test.

Reply Date: 2020/11/30

More Info

The RPR (Rapid Plasma Reagin) test is a non-treponemal test used to screen for syphilis. Its reliability is generally considered to be good, with a sensitivity of about 86% and a specificity of approximately 98%. This means that while the test is quite effective at identifying those who do have syphilis, there is still a chance for false negatives and false positives.
In your case, receiving non-reactive results at 80 and 90 days post-exposure is a positive sign, suggesting that you likely do not have an active syphilis infection. However, it is crucial to consider the window period of the RPR test. The test may not detect syphilis in its early stages, particularly within the first few weeks after exposure. The CDC recommends that if a person has had a potential exposure to syphilis, they should be tested again at three months post-exposure to confirm their status.
If you are considering retesting, it is advisable to wait until at least three months after your last exposure. This means you should ideally test again in the third week after the three-month mark, which would be around 13 weeks post-exposure. This timing allows for the antibodies to develop sufficiently for the test to yield accurate results.

It is also important to note that while RPR is a useful screening tool, it is not definitive. If you receive a non-reactive result but still have concerns about potential exposure, it may be prudent to follow up with a treponemal test, such as the TPHA (Treponema pallidum hemagglutination assay), which can confirm the presence of syphilis antibodies.
In summary, while the RPR test is generally reliable, it is not infallible. Non-reactive results at 80 and 90 days are encouraging, but retesting at the appropriate time is essential for peace of mind and to ensure accurate diagnosis. If you have any lingering concerns or symptoms, consulting with a healthcare provider for further evaluation and testing is always a wise course of action.

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