[Question #5109] Fourth generation testing

25 months ago
Hi,

My questions are:

 1. the accuracy of a combined hiv test (antibody/antigen) at 28 days?

2.is it to early to have ars symptoms show up between 4 and 5 days after an exposure? 

3. Can I move on with my life after a negative combined hiv test at the 28 day mark post exposure? I also had a combined test at 7 days post exposure which was negative..
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
25 months ago
Welcome to the forum. Thanks for your succinct question. It would be helpful to know about your exposure and how risky it might have been. Test results should never be viewed in a vacuum, but only in connection with other factors that influence interpreation of the results, like exposure history or symptoms. Tha being said:

1) These tests detect 98-99% of HIV infections at 28 days.

2) Symptms at 4-5 days are too early. (What synptoms did you have?)

3) To some extent, this depends on the expousre and your symptoms. But to be 100% conclusive, have another AgAb test 6+ weeks after exposure.

Happy to comment further if you want to provide more details. In the meantime, I hope these comments are helpful.

HHH, MD
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25 months ago
Thank you for your answers.

I had an exposure in Bali with a sex worker.. I was wearing a condom and believe it stayed intact... my symptoms were sore throat, headache and night sweats which occurred around 6 days after exposure.. from what I have read this was far too early for symptoms..  Would you agree?

98-99% at 28 days sounds almost certain to me that hiv was not the cause of these symptoms? 

Have you ever heard of someone having a negative combination test at 28 days that has later changed with another test? 
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
25 months ago
Given the condom protection, the chance you acquired HIV was nil or close to it. And indeed your symptoms were pretty early -- generally ARS symptoms don't start before a week and usually not until 10-14 days after acquiring the virus. That said, I certainly understand your concern and agree it was wise to be tested to be on the safe side.

Although the test is "only" 98-99% reliable 4 weeks after expsoure -- i.e. very good but not quite perfect -- it IS 100% proof your symptoms were not due to ARS. Everybody who has ARS, or had it, always has positive antigen-antibody (combo) test resutls. You cannot have ARS without teh 4th generation test being positive.

I have never had any patient with negative AgAb at 4 weeks who turned out to have a new HIV infection after all. The statistics tell you it can happen (i.e. 1-2% of the time). Considering your overall situation, I am very confident you do not have HIV. However, you could consider a repeat test at 6+ weeks to make it that much more certain.

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25 months ago
Thank you for being so quick at replying.

So are you saying that anyone who has early symptoms would have positive results sooner? It is good to know how accurate these fourth generation tests are, they sound very sensitive to the virus. 

I have read allot of doctors say that the tests are 95% accurate at 28 days but a small amount of people have delayed response.. what would cause these delayed responses? 





H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
25 months ago
The symptoms of ARS are due to the body's immune response to the virus. Within a week of onset of ARS symptoms, testing is positive. As far as is known, there are no exceptions. For example, if onset of typical ARS symptoms at, say, 10 days, by 14-15 days the AgAb test would be positive. (Note that the it's not the case that all people remain negative for nearly 4 weeks and everyone's test becomes positive at that time. Some people have posiitve tests as early as a week after exposure. It take 4 weeks to reach 98-99% and 6 weeks to reach 100%.

Therefore, it's more like 98-99% accurate at 4 weeks, not 95%. The reasons that 1-2% remain negative at that time aren't known. One possibility is that the people in the research studies of test performance had taken anti-HIV drugs and were not honest with the invetigators. (That would mean the tests actually pick up all infections by 4 weeks. But this is only a guess; in truth, we just don't know the reasons.)

That completes the two follow-up comments and replies included with each question, and so ends this thread, which will be closed shortly. I hope the discussion has been helpful.
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