[Question #10028] False Positive HIV Result?

26 months ago

Hi doctor, 30y Male. About almost 15 months ago I had a sexual encounter with a high risk CSW (it was a street pick up and looked like active drug user). The encounter was protected vaginal sex and protected oral sex (she gave it to me). The condom was bought at hotel lobby and I dont really know what kind of condom it was (lambskin, latex, or else) and I didnt really check for any holes afterwards. Just remember that I took the condom off when finished and it seems in one piece.

Over the last year I've had numerous HIV tests, maybe 10 or 12 tests. In my country there are 2 main labs, one does a 4th gen Ag/Ab test (according to them) and the other only offers a Antibody only test, so this last one I've mixed it up with a Antigen P24 standalone test.

All these tests results were negative over the last year, maybe 5-6 Ag/Ab HIV tests, and 2 combinations of Antibody + P24 tests (this last ones at 6 and 9 months).

I even had a PCR HIV test done at 5 months with undetectable results.

At 12 months post exposure I went again and tested with the combination of Antibody only test + Antigen P24 test, but in this case the Ab test was negative and the Antigen P24 test was positive with a value of 5.5 vs. cut off value 3.0. I immediately went to and ID specialist and one week after this results I repeated a Ag/Ab test, negative and had a Western Blot, negative (including P24 negative) and a HIV PCR, also negative. I understand that the standalone P24 test could be more specific for this antigen than any other combined test, so:

26 months ago

1) Could this be that the test is detecting something that other tests still cant at this stage?

2) Is this definitely a false positive or it could be an accurate result? My doctor believes so because of negative Ag/Ab, Western Blot and PCR test.

3) If I indeed contracted HIV 15 months ago, what symptoms would I be having? My ID doctor believes I would at least be experiencing some swollen lymph nodes. I have none. But I've been struggling with GI issues for almost a year now.

4) My partner has been recently complaining a lot about feeling unwell, could this be related?

5)How could I put this behind me? Should I retest now almost 3 months post the positive antigen result to clear anything out? Im worried about another false positive result or worse, a true positive.

6) Could the Western Blot or PCR tests be mistaken? Mostly if it is the case that Im just starting right now to develop P24 antigen which would be mean Im just starting acute infection (I dont know if thats possible one year post exposure)

H. Hunter Handsfield, MD

26 months ago

Welcome to the forum. Thanks for your confidence in our services.

I'm sorry to hear about your false positive p24 antigen test. I'm sure it was alarming. However, it clearly was a false positive result and you can be completely confident you do not have HIV. From your description, it sounds like you have had excellent care by your ID specialist, who likely knows as much about HIV diagnosis and testing as I and Dr. Hook do. I'll also add that you describe a very safe sexual lifestyle in regard to HIV: had I been your doctor when the positive test result happened, I would have immediately suspected it was false positive. To your specific questions:

1) The reasons for false positive HIV test results, either antigen or antibody, are unknown. It isn't because you have something that other tests are missing. Probably it happens mostly because of biochemical issues in the test itself.

2) I agree with your doctor. It is not possible you have HIV.

3) Here too I agree with your doctor. However, the symptoms really aren't important anyway. HIV test results always overrule symptoms, no matter how typical they seem to be for a new HIV infection.

4) Almost certainly your partner's symptoms are not due to HIV and are unrelated to your other sexual exposures or to your false positive p24 antigen test.

5) You can "put this behind" now. There is no need for further testing. If you remain anxious about it, I suggest discussing it further with your ID consultant; or consider professional counseling if that doesn't resolve your fears.

6) No, there is no possibility that you have HIV. It never takes more than 3-4 weeks for true p24 antigen to develop and be detected by testing.

In summary, I'm happy to confirm all you have been advised by your ID consultant. All is well and I hope these comments help you move on with no further worry. Let me know if anything isn't clear.

HHH, MD

---
---
---

26 months ago

Hi doctor, thanks for you answers, its very reassuring.

Even though my doctor conclude my test was a false positive, this was not his first impression. He actually believed I could be just starting to present P24 Antigen one year after my encounter. This is what troubles me, in my country it seems like in medical practice we are still out of date. Labs suggest to test after 9 months of exposure to have a final test, but most doctors do believe that HIV positive patients can remain negative in testing for a whole year, this is crazy right?

I don't know if it has something to do with technology in my country regarding testing that doctors believe this or is it just that they don't handle the current data, but it sure scares my a lot and then I got this "positive" result and its like "omg could people really turn positive after 1 year?"

To give some more context I have GI issues for almost a year, recently Ive been experiencing red dots on chest and face, my partner also. Both feeling uneasy.

1) You sounded pretty sure about my false positive test but with my partner you say "almost certainly not HIV" so you believe theres a chance?

2) If the P24 test was real, would the western blot or de 4th gen test detect the P24 as well with a sample taken 1 week later? Or is it possible that P24 already disappeared for the next week and not enough antibodies still developed to be found on test.

3) Can someone with HIV have undetectable PCR test 1 year after exposure without treatment? I have 2 undetectable PCR tests, one at 5 months and another one at 12 months.

4) In the hypothetical case that I didnt wear a condom in this encounter and it was vaginal unprotected sex with high risk CSW, would you still believe Im HIV free at this point?

H. Hunter Handsfield, MD

26 months ago

I'm not aware that it's ever possible to first have p24 detectable more than a few weeks after exposure to HIV. We try not to overtly disagree with what users report about their own doctors' advice and treatment, but I have to disagree with your doctor on this. And certainly with the modern HIV blood tests -- in particular the AgAb ("combo", "4th generation") blood tests, there has never been a proved case of HIV in which to took more than 45 days for positive test results. As for the technology in your country, I doubt it is any different than in North America or Western Europe: most other countries have adopted the very same tests, or very similar tests even if developed locally.

1) From my perspective, there's always the possibility that someone's partner has had sexual exposures that the user doesn't know about. My "almost certainly" comment left open the possibility that your partner could have HIV, but not from you. I'm not suggesting she (or he) has other HIV risks, only that I have no way to know.

2) Both WB and the AgAb (4th gen) test would have detected your infection if your p24 result were real.

3) On rare occasions, lucky persons with HIV are "elite controllers". Their immune systems are unusually effective in controlling HIV and they can have negative PCR tests. However, the other tests (AgAb, p24, etc) are uniformly positive.

4) Test results always overrule exposure. And even unprotected vaginal sex is less risky than most people realize. If a woman has HIV, the average transmission risk to a male parter is once for every 2,500 episodes of unprotected vaginal sex. And of course you don't even know your CSW partner had HIV anyway. Most CSWs do not. So even if you had an unrecognized condom failure, you were at little risk. In any case, you can trust you current test results.

---
---

26 months ago

Thank you doctor.

1)So no matter the risk and possible symptoms me and my partner may have now, I can be 100% sure I dont have HIV? Can I keep having sex with my partner without the fear of infecting her?

I should point out that Ive been experiencing a lot of mouth ulcers as well.

2)At the time of the P24 positive result, I was experiencing a flu/cold and someone very close was positive to COVID, do you think this could be the cause?

3) Is the WB better or worse than the P24 test? What result is more reliable the positive P24 on the standalone test, or the negative P24 on the WB? What I tried to asked before is if it is possible that in that 1 week timeframe between tests, P24 could have lowered to undetectable levels but still not enough antibodies to be detected, making the other tests false negative?

4) Do you think Im at risk for any other STIs? Ive tested negative for most STIs after the window period and negative to Chlamydia and Gono through urethral swab and urine test, but I keep having a lot of genitourinary symptoms like penis pain, testicular pain, urine difficulty, some clear discharge

H. Hunter Handsfield, MD

26 months ago

1) Yes. You "cam be 100% sure [you] don't have HIV."

2) It is impossible to have symptoms caused by HIV and have negative results for p24 antigen, as well as the other negative tests you have had.

3) WB is a older technology, not considered as reliable as more recently developed tests. In your case, the combination of all results prove you do not have HIV. That one type of HPV test is negative does not change the reliability of other tests.

4) You describe a sexual exposure unlikely to transmit any STD, not just HIV. The symptoms you describe are most consistent with anxiety, and I see no clear need for testing. However, if you will feel better knowing you have had negative test results, and if testing has not been done yet, consider a urine test for gonorrhea and chlamydia and a blood test for syphilis. If you do it, you can expect negative results. If your genitourinary symptoms continue, it would make sense to see a urologist -- not because of a likely STD, but for other explanations for these very common symptoms.

That completes the two follow-up exchanges included with each question and so ends this thread. I hope the discussion has been helpful. You definitely can move on with no further worries about having HIV or other STD.

---