[Question #3481] Hiv tests 4 and almost 6 weeks

37 months ago
Good day Dr, My name is Martin and I am writing from Poland. I have a condom break with a CSW here in Poland. The CSW is at moderate risk for HIV as she gets extra cash for unprotected sex and does drugs ( probably not IV drugs, but she snorts cocaine). I had a HIV AG/AB test from Abbott  at 29 days post exposure  - it is a 4th generation test to my knowledge. At day  40 I had a finger prick rapid test - LABMEN ANTI HIV 1/2 at one of Poland's HIV/AIDS clinics. I was told that antybodies for this last test start to appear at  8 weeks (???) and the test is useless at this point.  My questions: 1. Is it possible/ or you ever heard about rapid tests looking only for one type of antybody,not for all antybodies,? 2. Can I consider this 2 tests at this time points to be at least 98-99 % accurate?? 3. Should I re-test and when?? Thank you
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
37 months ago
Welcome to the forum. Thanks for your question and for your confidence in our services.

The most important thing is that you have had two nearly 100% conclusive tests. The Abbott AgAb (4th generation) test is around 99% conclusive at 4 weeks (and 100% by 6 weeks). I'm not familiar with the antibody test you had, but most such tests are 95-98% conclusive at 6 weeks (40 days). (It is nonsense that such a test result is "useless". It is not true that antibodies do not "start to appear" until 8 weeks. Antibody always starts to appear at around 10 days, then takes a few weeks to be 100% detected. 

So let's do a quick calculation. Let's say there's 10% chance your partner had HIV. (Probably it was a lot lower than that -- I doubt any higher than 1%.) The average HIV transmission risk from a single episode of unprotected vaginal sex is around 1 in 2,500. (Actually, it probably was a lot lower, assuming you stopped sex right away after the condom broke.) So even before you were tested, the chance you caught HIV was no higher than 1 chance in 25,000. Now let's assume your AgAb (Abbott) test detects about 99% of infections at 29 days. That negative results means the possibility you have HIV fell to 1 chance in 2.5 million. The rapid antibody test at 40 days probably was about 95% reliable -- so that result doesn't help much, although it does tend to confirm the negative result of the earlier Abbott test.

To your specific questions:

1) The test you describe clearly detects at least two antibody types, one each for HIV1 and HIV2. Beyond that, I have no knowledge of that test's biology. However, Poland is a medically sophisticated country, and I would think the HIV/AIDS clinics are technically competent and use reliable tests. (Even though the technician you spoke to apparently misunderstand's the test's window period, or you misunderstood him or her.)

2) Yes, your results so far are 98-99% reliable. This does NOT mean there is a 1-2% chance you have HIV. As calculated above, the possibility you have HIV is under than 1 chance in 2.5 million and maybe as low as 1 in 25 million.

3) Have another AgAb test at 6 weeks; or another rapid test at the clinic 3 months after the exposure. You definitely can expect the results to be negative.

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

HHH, MD
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37 months ago
Doctor, thank you for the professional advice and help. Just have a comment and 2 additional questions.  The person I spoke to was certificated advisor to conduct pre and post tests advice. Here in Breslau( Wrocław) we can do all the tests anonymously and for free. When I told him that I have read here on the forum that there were situations where 4th Generation tests sometimes can change from negative to positive after 4 weeks - he said that they have never encountered this and though in Poland official rule for any test is 3 months, they tell people that these negative results don't change. He said that for him it is a new piece of information and he is going to inform a National Center for HIV/AIDS in Poland about the issue.
Questions:
1. Is a finger prick rapid test as accurate at 40 days as a laboratory test looking only for antybody ( for example - ELISA test) ?
2. Would a rapid finger prick test be 100 % conclusive for me at 8 weeks or need to wait for 3 months?
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
37 months ago
Thanks for the follow-up information. I agree exactly with the advisor you spoke with. I too have never seen anyone with a negative AgAb test at 4 weeks who later turned out to have HIV and had a later positive test. However, there are published data showing that in rare cases it can take 6 weeks, which is why on this forum we advise 6 weeks as conclusive. https://www.ncbi.nlm.nih.gov/pubmed/29140890

1. The rapid, finger-stick blood tests are generally considered equally accurate as the lab-based tests.

2. Conclusive at 8 weeks (see the same citation as above), but official advice for many agencies probably remains 3 months.
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37 months ago
Dr, just my last comment and questions.  This link: https://smartsexresource.com/health-providers/hiv-tools   - provides possibility of false negative test on the exact day after exposure to HIV. From my knowledge and a question I asked on the website - this is somewhat official quidelines in Canada based on the study conducted by Taylor D. and others, which can be found in references on the website. It states that probability of false negative duo test at 28 days is 8 %. However the same calculator displays that DUO test at day 40-41 has the same accuracy as and ordinary antibody test, which I believe is not possible.  On day 28th plain antibody test is to have 13 % of false negatives. So not a very big difference to the DUO at 28 days when an antigen p24 peaks. It looks like this study was largely based on mathematical modeling and analysing which can mean not much in the real life.  I remember Dr Sean Cummings from Freedomhealth in London saying on their forum, that in his career I has seen few cases of negative DUO at 28 days turning later to be positive, but they were always not sure about the timing and the extent of exposure, in these cases. In other words the patients could have provided false info. Maybe my last question, therefore be interesting for other readers of this forum and for my personal interest. Is these few cases with changed DUO results beyond 28 days according to CDC - were they real life cases of people or was it based of some study and mathematical modeling??
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
37 months ago

Interesting website; I was not previously aware of it. I can't say what database(s) is has used to create it's calculator, but 8% false negative result for the AgAb test at 28 days conflicts with the latest published summary of test peformance (which I linked in my last reply), which has been endorsed by CDC (https://www.ncbi.nlm.nih.gov/pubmed/29140891). Like Sean Cummings and Freedom Health, I have never had (nor heard of) any patient with negative 3rd gen HIV antibody test at 6 weeks, or negative AgAb test at 4 weeks, who later had a positive result and actually had acquired HIV at the exposure s/he was concerned about. On that basis, previously published data, and the policies of some experts (e.g. Freedom Health) and public health agencies, on this forum we considered 4 weeks conclusive for AgAb, but changed to 6 weeks when these publications became available. (In fact, they really say 45 days for conclusive results -- but we round that off to 6 weeks.)


You are correct in your seeming understanding that the data really aren't all that precise. If you think about it, you'll understand it's very hard to accumulate substantial numbers of at risk persons with only one possible exposure event and test them regularly (e.g. weekly) for several weeks or even 3-4 months. I'm not sure of the exact methodology that was used, but I think you're probably right that it's a combination of real patients plus mathematical modeling.


That concludes two follow-up comments and replies and so finishes this thread. I hope the discussion has been helpful. The bottom line is that you were at low risk of infection (the risk is always low, under one chance in hundreds, for even the highest risk sexual exposures), and with your current results you can be confident you weren't infected. A final AgAb test at 6+ weeks would be strictly for reassurance; I'm confident it would be negative.

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