the Likelihood of False Positive TPHA Results in Blood Tests

What is the likelihood of a false positive result for the TPHA test?

In January, I donated blood and tested negative.
However, in August, I was informed that my TPHA was positive and RPR was negative.
In November, I went to the infectious disease department for testing, and the results were still the same: CIA positive with a value of 10.19 and RPR negative.
I have no symptoms of syphilis and have not engaged in sexual activity during this period.
However, the infectious disease doctor insisted that a false positive is impossible and that I must have had syphilis in the past and recovered.
I saw Dr.
Chen's response to someone else stating that TPHA can indeed have false positives; how low is that probability? Why does the infectious disease doctor say it is impossible? Is it because the value of 10.19 is very high? I have a history of allergies and atopic dermatitis, and I currently have obesity issues.
I have thought about some illnesses that occurred during this time; could they possibly cause a false positive? In March, I had cold symptoms (coughing for over a month, suspected mycoplasma), obesity, fatty liver, hepatitis, atopic dermatitis, colon cancer? (not yet tested) Leptospira (exposure to sewage and stray animals), in May I was stung by a bee, received a tetanus shot, and in July, I was diagnosed with COVID-19 (with pneumonia).
Could Helicobacter pylori be a factor? (gastroesophageal reflux)

Xianxian, 30~39 year old female. Ask Date: 2022/11/10

Dr. Chen Bozhang reply Family Medicine

Hello! Syphilis infection typically enters the body through skin and mucosal lesions, but it is primarily transmitted through sexual intercourse; sharing bathroom facilities, kissing, hugging, and similar activities in daily life do not pose a risk.
According to the self-reported test results, a negative RPR and a positive TPHA indicate "previous infection with Treponema pallidum, but currently no active infection, posing no risk of transmission to others." You can continue to monitor for any discomfort and decide whether to seek medical attention.
Thank you.

Reply Date: 2022/11/10

More Info

The situation you are describing involves a complex interplay of serological testing for syphilis, specifically the Treponema pallidum hemagglutination assay (TPHA) and the rapid plasma reagin (RPR) test. Understanding the implications of these results is crucial for accurate diagnosis and management.

Firstly, let’s clarify the tests involved. The RPR test is a non-treponemal test that detects antibodies that are not specific to Treponema pallidum, the bacterium that causes syphilis. It is often used for screening purposes. A positive RPR can indicate syphilis, but it can also yield false positives due to various conditions such as pregnancy, autoimmune diseases, or other infections. Conversely, the TPHA is a treponemal test that specifically detects antibodies to Treponema pallidum. A positive TPHA indicates a past or present infection with syphilis, but it does not differentiate between active and resolved infections.

In your case, the sequence of results shows a positive RPR and a negative TPHA, which raises the possibility of a false positive RPR. The fact that your RPR was positive twice, while the TPHA remained negative, suggests that you may not have an active syphilis infection. The negative TPHA indicates that there is no current or past infection with Treponema pallidum, which is consistent with the absence of symptoms and sexual activity during the period in question.

Regarding the likelihood of false positive TPHA results, it is important to note that while false positives can occur, they are relatively rare. The specificity of the TPHA is high, meaning that if it is positive, it is more likely to indicate true exposure to Treponema pallidum rather than a false positive. However, certain conditions, such as autoimmune diseases, can potentially lead to false positive results in treponemal tests, although this is less common.

The physician's assertion that you must have had a past infection is likely based on the high TPHA value (10.19). High titers can sometimes suggest a more recent or active infection, but they can also reflect a resolved infection. The lack of symptoms and the negative RPR further support the idea that you may not currently be infected.

As for your health concerns, the various conditions you mentioned (e.g., allergies, skin conditions, obesity, and past infections) are unlikely to directly influence the TPHA results. However, chronic illnesses and immune system responses can sometimes complicate serological interpretations.

In terms of your partner's health, if you are not currently infected, there is no need for concern regarding transmission. However, it is always advisable for partners to undergo testing if there is any uncertainty about sexual health.

In summary, your test results suggest that you do not have an active syphilis infection. The positive RPR may be a false positive, while the negative TPHA supports the absence of syphilis. If you have ongoing concerns or symptoms, it is essential to follow up with your healthcare provider for further evaluation and possibly additional testing to clarify your health status. Regular check-ups and open communication with your healthcare provider are key to managing your health effectively.

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