[Question #1363] Confused about HIV test results.

82 months ago



Thank you for taking the time to answer my question.  Let me provide a little background on my situation.


In September of this year, I cheated on my girlfriend when I had sex with a CSW.  We used a condom, but I noticed afterwards that the condom had broken.  After this act, I broke up with my girlfriend and I started to have anxiety that I may have contracted HIV.  I do not know the HIV status of the CSW.  12 days after my sexual encounter with the CSW, I had a 4th generation ag/ab  test done, and that came back negative.  Then, at 42 days after my sexual encounter with the CSW, I took another 4th generation ag/ab test that also came back negative and non-reactive.  At that time, my doctor told me that the results were conclusive.  To confirm that these results were in fact conclusive, I called the department of health for my region to ask about testing, and they confirmed that my results “should” be conclusive.   After receiving this confirmation from my doctor and the department of health, my girlfriend and I got back together, and we resumed having regular sex.


Since then, I have developed a resurgence of anxiety and doubt over my test results.  I started to do research online, and I have found some conflicting sources that state that a 4th gen ag/ab test is conclusive at 28 days, another source that 4th gen ag/ab tests are conclusive at six weeks, and many more sources, including the CDC, that state that 4th gen ag/ab tests are only conclusive at 3 months.  The conflicting information has me confused and concerned.  Now, I am concerned that my test results may have missed my seroconversion window period, and that the test results at 42 days were not conclusive, and that I should have waited for a 3 month test.  Additionally, now at 8 weeks, I have developed a sore throat with some sinus congestion that I have begun to attribute to ARS symptoms.  Finally, I am extremely worried that I may have infected my girlfriend.


My questions are as follows:


1. Is my 42 days 4th generation ag/ab test absolutely conclusive?

2. Is it possible that the 42 day 4th generation ag/ab test missed my seroconversion window period where my p24 levels and antibody levels were too low to detect (sometimes referred to as a “second window period”)?

3. Should I retest at 90 days?

4. Is it possible to experience ARS sore throat and sinus congestion symptoms after 8 weeks after my exposure?

5. Is it possible that if my tests were not conclusive or were a false negative, that I could have infected my girlfriend?

5. If my tests are conclusive, can I continue to have unprotected sex with my girlfriend?

H. Hunter Handsfield, MD
82 months ago
Welcome to the forum. Thanks for your question. Once in a while a question offers an opportunity for a blog-like reply that can be used in replying to future questions. I'm doing that now, perhaps with more detail than you might want. But bear with me.

In interpreting and providing advice on HIV tests, all agencies have access to the same data. So why the differences? It's basically a regulatory issue combined with various agencies attitudes toward legal protection. The science clearly supports 4 weeks as conclusive for the 4th generation (antigen-antibody) tests. There are three kinds of science here:  the known biology of HIV (when antigen appears in the blood then sometimes disappears, when antibody appears, and so on); reported results in patients at risk for HIV; and the reports of physicians who provide care. The last is quite important but difficult to quantitate:  but the truth is that Dr. Hook and I are not aware of any actual cases of people who had negative 4th generation tests at 4+ weeks who later turned positive and in fact had HIV contracted at the exposure in question. That this has apparently not happened at all, among the roughly 40,000 new cases of HIV diagnosed each year in the US, should be very reassuring.

Nevertheless, regulatory agencies like CDC do not like to rely on such "soft" data, which are difficult to confirm, and their legal teams advise reliance on the "official" test performance documented in pre-marketing research plus the package insert information as approved by the US Food and Drug Administration. Hence CDC sticks with 3 months (even though there are no better data on test performance at 3 months than one month), whereas others may go with 6-8 weeks.

Your question 2 reflects an urban myth and basic misunderstanding about how the test works. There is no "second window period". It is the antibody to HIV that clears p24 antigen out of the blood. In other words, you cannot have antigen disappear, making the test negative, unless antibody is present -- which makes the test positive. Once someone has a positive 4th generation HIV test, the result remains positive for life.

So that's the scientific background. As already implied, Dr. Hook and I are very confident about the 4 week (28 day) conclusively.

In addition, I would point out you had a low risk exposure. The vast majority of CSWs in the US do not have HIV (average 1 in a thousand or thereabout, certaiinly under 1%); and the average risk of transmission by unprotected vaginal sex, if the woman has HIV, us around 1 in 1,000. So even before you were tested, the odds you caught HIV were in the range of 1 in a million (0.001 x 0.001 = 0.000001). If we now assume your HIV test was "only" 99% conclusive, that brings the odds you caught HIV to 1 in a 100 million (multiply the previous result by 0.01). I hope you would agree that one in 100M is zero for all practical purposes!

To your specific questions:

1,3) Your 42 day result was "absolutely conclusive" and no further testing is needed.

2) See above.

4) ARS symptoms cannot start more than about 20 days after infection, and it is not possible to have ARS symptoms at 8 weeks without having a positive HIV test.

5) Noit possible.

6) Yes, you can safely have unprotected sex with your gf. You probably could have done so from the vary start -- and for sure after your negative test result at 42 days (or 28 days if you had done one at that time).

I hope this information has been helpful, but let me know if anything isn't clear.


82 months ago

Thank you.  That was very clear, and the science makes sense to me. 

My follow up question is just some clarification on the p24 antigen.  I have read that it takes about 10-20 days for HIV to replicate and for the p24 antigen to appear in your blood.  How late will it take p24 to show up in your blood?  Is it possible that HIV remains dormant for more than 28 days only to begin replication at a later time?  Is it possible for p24 to remain non-existent or low enough to remain undetectable for more than 28 days?  I know the 4th gen ab/ag test is supposed to test for both the p24 antigen and the HIV antibodies in a combination test.  But, is it possible that p24 does not become detectable until after the 28 day mark?  

Thank you again for answering my questions.
H. Hunter Handsfield, MD
82 months ago
It is not believed that delayed replication of HIV ever occurs; once infection is established, replication is believed to be immediate. Its pace is such that p24 typically appears in the blood within 10-12 days. I think 20 days is old news -- I'm not aware it ever takes that long -- and for sure it doesn't take 28+ days. The only exception might be when post anti-HIV drugs are given for exposure prophylaxis (PEP), but as far as I know, even this has not actually been reported.

Don't look for exceptions to the rule. As noted above, you were at exceedingly low risk for HIV even before you were tested. With the negative test results you have had, there is no realistic possibility you have HIV. It shouldn't be an issue for you.