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Accuracy of rapid tests?
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Accuracy of rapid tests?

Hi...I don't know who will get this question but I am wondering about a post that Dr. HHH made today. My question is in reference to this thread:

http://www.medhelp.org/posts/HIV-Prevention/Re-HIV-Testing-Clarification/show/1315890?personal_page_id=156410#post_6019573

My questions are:

1. Does this mean that all rapid tests are only 85% accurate? Or does this mean that they are only 85% accurate  within the window period vs. whatever percentage they were before?

2. The referenced thread states that they have recently discovered that Oraquick Advance tests have more false negatives than originally thought, is this the case for all rapid tests or just the Oraquick? Does this count for Unigold tests?

3.My partner and I both took rapid blood tests in June of this year and the results were negative. We took the tests 10 months after our last exposures, can I trust these test results or are they only 85% accurate? The tests we took were Unigold brand.

Thank you for taking the time to read this...before I had my test taken I worried about having HIV for 4 years and I just want this to all be over.
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Welcome to the forum.  Thank you for the opportunity to clarify a confusing situation.  My response in the thread cited was not carefully stated.

The concern about sensitivity of the rapid HIV tests, i.e. missing some infections, applies primarily to early HIV infection.  In people who have acquired HIV only a few weeks earlier, the rapid tests apparently miss more infections than the lab-based ELISA tests due.  85% sensitivity is only a rough estimate, and it applies primarily to OraQuick.  The other rapid tests have not been carefully studied in this way, but probably are closer to 90-95% sensitive.  However, even for established infection, the rapid tests miss a few infections that are detected by the lab-based (ELISA) tests.  In addition, the rapid tests are more often falsely positive than the lab-based tests.  THIS IS NOT NEW INFORMATION.  THESE FACTS HAVE BEEN KNOWN EVER SINCE THE RAPID TESTS WERE DEVELOPED, i.e. 10-15 years.

For theser reasons, the rapid tests are intended to be used when the lab based tests are impractical -- for example, if sophisticated labs are not readily available (like in many developing countries) or when patients may be difficult to contact with their test results, e.g. in emergency departments, and in STD clinics where patient populations are very mobile and many clients may not call or return to get their test results.  The rapid tests were never intended primarily for use by people who just want their results early, i.e. who are anxious and just don't want to wait a few days for their results.

Another point that Dr. Hook and I have made many times and needs to always be remembered:  Test performance alone does not determine the likelihood someone has HIV.  If the risk is low, e.g. with only 1 chance in 100,00 that someone caught HIV -- i.e. for the large majority of persons who post questions about possible exposures on this forum -- a test with "only" 90% sensitivity changes the odds that the person actually caught HIV to 1 in a million.  That ought to be highly reassuring, and it is wrong to focus on the 90% figure (or maybe "only" 85%) with any kind of alarm.

Those comments address questions 1 and 2.  As for question 3, by 10 months after exposure, all the rapid tests probably pick up 95% or more of all HIV infections, maybe approaching 99% or greater.  Assuming your HIV risk was low to start with; adding the fact that you apparently feel healthy, which is itself evidence against HIV of 4 years duration; and the test performance, you can be very certain you don't have HIV.  But if you want absolute certainty, a lab-based HIV test is always preferable to a rapid test.

I hope this helps you (and others) put these issues in perspective.

Best regards--  HHH, MD
8 Comments
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Avatar_f_tn
So I can't be sure that I am negative? Do you suggest re-testing?
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580755_tn?1357673215
Can you be sure...yes and no. Yes because the precentage is probably as Dr.HHH said 95%-99%, no because 95%-99%. Testing at this point would be for your own mental health as your risk was low, partner tests negative. Odds are probably more then 1 in a million that you would have HIV.
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580755_tn?1357673215
I just want to check and see if this is correct or written incorrctly?

" As for question 3, by 10 months after exposure, all the rapid tests probably pick up 95% or more of all HIV infections, maybe approaching 99% or greater."

10 months really or were you thinking 10 weeks?
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239123_tn?1267651214
"So I can't be sure that I am negative? Do you suggest re-testing?"  Did you read my reply?  I haven't changed my mind and I'm not going to repeat myself.

It turns out that Dr. Hook is aware of a research study, soon to be published, that examined the performance of rapid tests in detail.  The approach is called a "meta-analysis", meaning they carefully analyzed al the previously published research studies and came to an overall conclusion.  The study concludes that dual rapid blood (not oral fluids) testing, using the tests produced by any two different manufacturers, give results equally reliable as lab-based ELISA testing.  My comments above remain valid for any single rapid blood test.

Vance:  I was responding to bebe1005's question about being tested 10 months after exposure.  Probably it would be the same any time ~8 weeks or more after exposure.
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Avatar_m_tn
Doc this info is killing us(by us i mean overanxious ppl)
In my case, I got tested probably with a rapid test (the microbiologist told me that he tests the samples on his own and he has a small place + the results were given to me after some hours) 3.5 months after the last unprotected encounters and 2.5 months after a fingering incident while having dermatitis on my hand (not a severe case though).
Even if i exclude the second incident which i can do, how can i keep on with an 85% result after experiencing different symptoms, which im not even going to describe given that i know your answer!
I am not posting for a risk evaluation, it is just the 85% which i previously considered to be closer to 100.
please answer to this because it sounds as a highly debatable matter.
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Avatar_m_tn
I don't need an answer and don't want to be rude but you advise people to test at 8 weeks for a conclusive result and then you say that rapid tests are only 85% reliable. How could that be?
In your response to bebe you said that concern about sensitivity of the rapid HIV tests, i.e. missing some infections, applies primarily to early HIV infection, and after that you said that his/her test 10 months after exposure was only 95% reliable... Am i missing something??
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239123_tn?1267651214
OK, folks:  Listen up!

Re-read all my comments above, concentrate on them.  Remember two things:

1) If you are concerned about having a new HIV infection, request a lab-based test, not a rapid test.

2) If you have a rapid test anyway, put the results in context.  Even a result that is "only" 85-90% reliable is HIGHLY REASSURING, especially if your HIV risk was low (e.g. most heterosexual exposures, condom protected sex, oral sex, etc).  If it is not highly reassuring to you, it is your problem, not the test's problem.  The combination of a low risk exposure plus a negative result is virtually 100% proof you were not infected.  Believe it.  If you cannot, ask your doctor to do a lab-based test in addition to the rapid test.

That's the end of this thread and end of this discussion.
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Avatar_m_tn
A related discussion, I thought 6 to 8 weeks was good. was started.
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This Forum's Experts
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H. Hunter Handsfield, M.D.Blank
University of Washington
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Edward W Hook, MDBlank
University of Alabama at Birmingham
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