Syphilis Testing: RPR and TPHA Explained

Syphilis testing consultation

Hello Dr.
Hong, I have undergone RPR (STS) syphilis testing at 39, 111, and 270 days after engaging in unprotected sexual intercourse, and all results were negative (Negative, Non-reactive).
I would like to ask Dr.
Hong: (1) Does three negative RPR tests indicate that I am not infected with syphilis? (2) Do I need to undergo another type of syphilis test, such as TPHA? I am unsure if both RPR and TPHA tests need to be done simultaneously for accuracy.
Previously, I consulted with the testing personnel, and they mentioned that TPHA is considered a confirmatory test, so it is sufficient to only perform the RPR test after unprotected sexual intercourse.
I would appreciate it if you could take the time to answer my questions.
Thank you for your help.

JJ, 30~39 year old female. Ask Date: 2020/07/20

Dr. Hong Yuanbin reply Internal Medicine

Hello, the VDRL test can fluctuate with the onset or resolution of disease, so a negative result indicates that you have never been infected or that you have been infected but have since recovered.
However, one drawback of the VDRL test is that certain autoimmune diseases can also yield a positive result.
Therefore, the initial VDRL test should be confirmed with the TPHA test.
Once a person has been infected, the TPHA will remain positive even after recovery, so it is typically used for initial confirmation and does not need to be repeated.
Regarding your situation, you likely have never been infected or, although you were infected, you have since recovered.
If you choose to have the TPHA test, it is merely to confirm whether you fall into the category of "having been infected but now recovered." Clinically, this is also considered as "no syphilis," which is why the physician may suggest that it is not necessary to test for TPHA.
Thank you for your question.

Reply Date: 2020/07/20

More Info

Understanding syphilis testing, particularly the RPR (Rapid Plasma Reagin) and TPHA (Treponema pallidum hemagglutination assay), is crucial for accurate diagnosis and management of this sexually transmitted infection.
1. RPR Testing: The RPR test is a non-treponemal test that detects antibodies in the blood that are produced in response to substances released by damaged cells, which can occur in various conditions, including syphilis. A negative RPR result, especially when consistently negative over multiple tests, typically indicates that you are not currently infected with syphilis. In your case, having three negative RPR tests at intervals of 39, 111, and 270 days post-exposure strongly suggests that you have not contracted syphilis from the unsafe sexual encounter.

2. TPHA Testing: The TPHA test, on the other hand, is a treponemal test that specifically detects antibodies against the Treponema pallidum bacterium, which causes syphilis. This test is more specific and remains positive even after successful treatment of syphilis. It is often used to confirm a diagnosis when a non-treponemal test (like RPR) is positive.
Given your situation, where you have had three negative RPR tests, it is generally not necessary to perform a TPHA test unless there are specific clinical indications or if you have ongoing concerns about potential exposure. The TPHA test is often recommended if there is a positive RPR result or if there are symptoms suggestive of syphilis, such as sores, rashes, or systemic symptoms.

Why RPR Might Fluctuate: It’s important to note that RPR can sometimes yield false positive results due to various factors, including autoimmune diseases, pregnancy, or other infections. This is why a negative RPR result is reassuring, especially when it is consistent over time.
Testing Recommendations: In clinical practice, it is common to perform both RPR and TPHA tests for comprehensive syphilis screening, especially in high-risk populations or after potential exposure. However, in your case, the consistent negative RPR results provide a strong indication that you do not have syphilis, and further testing with TPHA may not be necessary unless new symptoms arise or if there is a change in your risk status.

Conclusion: In summary, based on your three negative RPR tests, you can be reassured that you are unlikely to have syphilis. If you have any lingering concerns or if your sexual health situation changes, it may be prudent to consult with a healthcare provider for further evaluation and possibly additional testing. Regular follow-ups and open communication with healthcare professionals are key to maintaining sexual health and addressing any concerns that may arise.

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