[Question #4115] HIV Test Window Periods

32 months ago
Hello,

My question pertains to HIV test window periods. I had a one night stand of unprotected vaginal and oral sex with a female coworker recently. I've taken two STD panels (HIV 1+2 AB/HIV 1p24 AG CLA; Trep. pall. Igg+IgM; Hep C; and chlamydia/gonorrhea urine) through Kaiser the first at 4 days after and the second 39 days after. All results negative from both panels. Both HIV tests were vein-drawn.

I've read and heard conflicting answers on window periods regarding this type of HIV test. Some say most people (%95) will test positive after 4-6 weeks. Others say it can be conclusive by 28 days. Yet I've also read and heard that only 3 months (sometimes 6 months) can be considered conclusive. What's the truth? Can I consider my results conclusive or should I take another test? If so, when? Today would be about 8.5 weeks (59 days).

Also, the doctor gave me a TDAP vaccine on the same day of the second test and I developed mild to moderate flu-like symptoms about 3-4 days later. Cough, sore throat, sneezing, body aches, headaches, feeling cold. I don't recall a fever, chills, or a rash but I felt pretty crappy overall. This lasted about 1-1.5 weeks. Would that vaccine affect the results? I don't know if those were delayed HIV symptoms, were a result of the vaccine, or a normal flu/cold. I'm a flight attendant so I'm in daily contact with many people.

This whole waiting game has caused me a lot of stress and the anxiety is eating me alive. I want to move on with my life but am constantly worried about this. Please help if possible.

Thank you in advance.
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
32 months ago
Welcome to the forum. Thanks for your question. It provides an opportunity for a slightly longer, blog-like reply that I can use for future similar question.

Indeed there remains confusion about HIV seroconversion intervals (window periods). Most of the confusion can be sorted out by considering the test type and when the tests were developed and first used. The earliest tests, which detect only antibody, i.e. the body's immune response to HIV, took up to 8 weeks and rarely 3 months to become positive, the origin of the initial advice for 3 months to conclusive results, sometimes extended to 6 months by conservative advisors. However, those original tests are no longer used, or only rarely. The main tests in use today are newer antibody tests ("3rd generation") and antigen-antibody (Ag/Ab, "combo", "duo", "4th generation") tests. Antigen measures virus, which appears in the blood first, as well as the immune response (antibody). For over a decade, these are the only tests in routine use in most settings, with a few exceptions mentioned below. The modern antibody tests are usually positive by 4 weeks and nearly always by 6 weeks, but may rarely require 8 weeks. The Ag/Ab tests almost always are positive by 4 weeks, but on rare occasions require 6 weeks, but never longer.

Agencies, physicians, etc who still advise 3 mo. either are simply behind the times, i.e. haven't updated their websites and brochures in the past 10-15 years, or simply hyper-conservative in their advice. For the Ag/Ab tests, 4 weeks was commonly advised until a year ago, when a comprehensive summary by CDC showed that it rarely can take 6 weeks -- hence that's the most accepted conclusive interval for those tests.

Apparent exceptions to the rules above:  Here and there older antibody tests ("second generation") still are used and may rarely take 3 months to conclusive results. The most common example that I know of is the Home Access test, wherein the user collects a blood specimen at home and mails it to the company. Even though the oral fluids antibody tests (Oraquick) technically is 3rd generation, the amount of antibody in crevicular fluid (the juices between gum and tooth) have much lower antibody levels than blood, and so these tests can take up to 3 months to become positive. Finally, when someone is taking anti-HIV drugs as pre-exposure or post exposure prophylaxis (PrEP, PEP), if treatment doesn't work -- i.e. they become infected despite treatment -- in theory it could take longer for the tests to become positive, so most experts recommend final testing at 3 months or even 6 months after PEP or PrEP. 

There are no medications, illnesses, or vaccines that alter the time to reliable HIV testing. That's not quite an urban myth, because at one time there was biological plausibility for such effects. However, if this occurs at all, it is (and always has been) extremely rare and occurred only with profound immune deficiencies, such as might occur with cancer chemotherapy or high-dose immunosuppression of the sort used after organ transplants. Even here, it's rarely a problem, especially with the Ag/Ab tests. If immune difficulties interfere with antibody production, antigen rises to even higher levels than otherwise. If anything, these tests might be more strongly positive in such persons, or positive sooner, not later. (At least that's the theory. But it's such a rare problem that nobody really knows for sure.) Certainly TDAP nor any other vaccine has any effect and neither do common colds or other infections that cause the symptoms you describe.

As for your exposure, it was very low risk for HIV to start with. In any case, all your test results were valid. The 4 day result was conclusive for gonorrhea and chlamydia, but meaningless for all the blood tests, except as a baseline to know you weren't infected before the exposure. But all blood tests were conclusive at 39 days. That's 3 days short of 6 weeks for the HIV tests, but given the near zero risk you were infected, it can and should be considered conclusive.

I hope this information is helpful. Let me know if anything isn't clear.

HHH, MD


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32 months ago
Thank you very much for the speedy and thorough reply, Dr. You answered all my questions and some.
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
31 months ago
Your doctor is wrong or you misunderstood her. It is nonsense that the AgAb tests are "useless" at 39 days. I stand by my original reply and have nothing more to say or any different advice to give.---
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
31 months ago
Your doctor is wrong or you misunderstood her. It is nonsense that the AgAb tests are "useless" at 39 days; a negative result at that time is roughly 99% certain to remain negative. I stand by my original reply and have nothing more to say or any different advice to give. When conflicting advice exists, it is the user's responsibility to make a judgment as to who the more reliable expert is, or to consider getting yet another opinion. But trust me on this:  nobody has EVER had a negative AgAb test at 6+ weeks after exposure and then go on to develop a positive result. In theory this might happen if the person received anti-HIV drugs for post exposure prophylaxis (PEP), but even that is theoretical with few if any actual known cases.  (All this assumes no reexposure to HIV, of course.) 
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31 months ago
Ok. Thank you.
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
31 months ago
Thanks for the thanks. You might also be able to help your physician in her understanding and advice to other patients. Consider printing out this thread, especially the main reply above, which (as I re-read it) is a highly accurate, science based summary of HIV test performance. And on reflection, I'm sure she will understand that one doesn't need 100% test performance to give 100% assurance that patients don't have that condition.

That concludes this thread. I hope the discussion has been helpful.
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