False Positive Results for Syphilis

[mrspreggo82]

Hi,

I am pregnant and went in for my first round of bloodwork. Everything came back great, except that my doctor said I had a positive syphilis test that was then followed up with two negative test results (RPR and TPPA). He said that it is most likely a false positive, but wanted me to do another round of blood work at a different lab. I spoke to another OBGYN who said I definitely don't have syphilis based on the negative follow up results. I have a few questions:

1. Is the FTA-AB test more accurate than the RPR and TPPA tests?
2. If I do have syphilis, will they be able to identify the stage that it is in and will I and my baby be able to be effectively treated?
3. Wouldn't I have had some symptoms at some point? I have been with my husband for 9 years, so i would have had to be infected before that...isn't 9 years enough time to see a symptom?
4. I had mono when I was a kid; would that cause a false positive?
5. My mother has RA, but I do not. Could this still through off results?

Thanks for your help!

[Edward W Hook, MD]

Welcome to our Forum. I'll be pleased to help. Unfortunately, there are no blood tests that do not have occasional false positive test results.  In the majority of cases, false positive tests are a chance event (i.e. just bad luck) although there are a few medical conditions in which people have increased rates of false positive tests.  These include pregnancy and rheumatologic illnesses such as rheumatoid arthritis and probably relate to the fact that the immune system is "turned on" in both conditions.  We reduce being misled by false positive test results by doing two, unrelated tests such as the RPR and TPPA or FTA.  If one test is false positive, the tests will disagree while if they are due to the disease being tested for (like syphilis), both tests are positive and therefore are referred to as "true positives".   Just to make things a bit more complex, some false positive tests are transient while in other cases they are lifelong.

I hope that these generalities are helpful.  i will now go to your specific questions:

1. Is the FTA-AB test more accurate than the RPR and TPPA tests?
No, it is not a matter of accuracy.  

2. If I do have syphilis, will they be able to identify the stage that it is in and will I and my baby be able to be effectively treated?
Based on your test results, I am confident that you do not have syphilis. If you did however, syphilis is readily treated in pregnancy to avoid consequences of the infection in both the child and the mother.

3. Wouldn't I have had some symptoms at some point? I have been with my husband for 9 years, so i would have had to be infected before that...isn't 9 years enough time to see a symptom?
Not all syphilis is symptomatic.  As I said above, it is far more likely that your results are falsely positive than that you have syphilis.

4. I had mono when I was a kid; would that cause a false positive?
If you had mono now it might lead to a false positive by turning on your immune system but past mono would not cause this. As I said, the most likely explanation is bad luck and a chance event.

5. My mother has RA, but I do not. Could this still through off results?
Perhaps. See above.

I hope these comments are helpful. It sounds like your doctor is doing all the right things for you.  I know that when our patients are pregnant we worry twice as muc as when they are not- that said, I am confident you will be fine.  Work through this with your doctor. EWH

[Edward W Hook, MD]

Thank you for the follow-up and pleased at the outcome, as I'm sure you are.  EWH

[mrspreggo82]

Just wanted to let you know that my second round of blood tests came back all non-reactive. My doctor suspects lab error or a false-positive the first time around. Needless to say, I am so relieved. Thanks again for your help!

[Edward W Hook, MD]

It is hard to predict but I suspect it will be.  I would be interested to hear.  Please let us know.  EWH

[mrspreggo82]

Thank you, Dr. Hook. Your explanations are very helpful. One last question: given my negative RPR and TPPA results, do you think that the FTA-ABS test is most likely to also be negative?

Many thanks!