[Question #3879] Understanding

34 months ago
Some questions

You have recently stated that oraquick or antibody testing has false negatives at the rate of 1 out 10 and 1 out of 20 respectively (presume non oral quick tests).


1. How can statements such as, "Antibody tests are conclusive at 6-8 weeks" if there is a 1 out of 20 chance that an antibody test would
be falsley negative?

2. That is a 5% chance on any given test, I am unsure how someone can live in confidence with a 5% chance their test could be wrong

3. How does false negative ratio apply on 4th generation tests?

4. Do the above ratios correspond to any specific time line? For example if someone tests during, then beyond the window period then the ratio 
will always remain at a 5%-10% (depending on which antibody test) chance the test will miss infection. When does a person then feel completely confident that they are fully conclusive?
Im confused

5. I will presume that these ratios are substantially lower with 4th generation tests?

6. I understand you make statements based on risk, chance and tests---- Let's assume someone has a very high risk and tests at 3 months/4months/5months/6months with a third gen test, you are telling me that there is and always will remain a 5% chance its wrong? 

7. I have seen statements such as, "no matter the risk the 4th gen tests are fully conclusive at 6 weeks" Are the above missed infections on antibody oral
and lab based tests only and doesn't apply to the 4th gen tests?

I guess the question is, how can statements on conclusivity be made if there are 5 to 10% chances that a test will be falsley negative?

Thank you and i am simply asking for clarity on your recent coments.
Edward W. Hook M.D.
Edward W. Hook M.D.
34 months ago
Welcome to our Forum.  I'll try to explain.  No medical test, none at all, ever, is perfect.  Good tests still rarely give results which are falsely positive or falsely negative.  We are trained to take steps to avoid accepting and acting upon incorrect tests.  Health care providers use tests as tools to help them evaluate their patients, combining those results with other elements of an evaluation such as whether or not signs and symptoms are present and what those signs and symptoms are, as well as other factors such as what a person's risk is for the outcome of concern.  Then they combine these factors with a statistical analysis of the probability that a test is truly positive, truly negative, falsely positive, and falsely negative.  On some occasions they also use additional tests, unrelated to the test first used to confirm their answer.  When all of these tools and techniques are used together, they provide very accurate results. 

For HIV tests, it is important to remember that in nearly all settings in which they are used to evaluate persons for new infections, less than one tenth of 1% and often far less than that proportion of persons tested have HIV.  Thus if you want to find 100 positive tests when 0.1% of people are infected you need to test 100 X 1000 or a total of 100,000 people at least to have 100 positive tests.  If the test misses 1 in 12 infections (the conservative estimate for Oral fluid HIV tests), then your hypothetical test would have detected 92 out of 100 tests and incorrectly told 8 out of 100,000 people they were not infected.  And this is the worst case scenario.  The odds of telling someone they do not have HIV get even lower when persons are tested more than once, when there statistical risk for infection is considered, etc. 

Thus, when clients on this forum ask about their risk for HIV our answers are based on consideration of all the information provided, not just test performance.  When a client asks about the "conclusiveness" of a test result and have provided the appropriate information, we put all the pieces together to provide our best assessment.  So, just as I cannot completely assure you that you will not be stuck by a meteorite falling from space today, when I consider all of the available data, I can say with great confidence that it will not happen. 

As I said above.  no test is perfect and some tests are better than others.  The oral fluid tests are popular because they do not require blood and can be done outside of professional laboratories.  They are powerful tools for providing information about HIV and we continue to endorse them for many of our clients.  They however are not as good as laboratory-based tests in general and, among laboratory based tests that test for both HIV antigen and HIV antibody are more accurate than tests which test only for antibodies.  Other  tests, like PCR-based tests have other problems such as falsely telling people the test is positive when it is not.  All are good tests when used in the right setting.  All have been judged to be appropriate for use on most settings by the CDC, the WHO and the U.S. FDA. 

I hope this information is helpful to you.  EWH
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34 months ago
Thanks Dr. Hook

1. If someone has tested 3 times using 4th gen tests after 42 days would you then say the are conclusive negative? Chances of three false negatives after window period out to 23.5 weeks?

I can understand perhaps 1 or 2 false negative tests but three?

2.  Would there be any reason one would need to test after almost 6 months if no new exposure and no anti hiv med was used?

3. I presume those figures were based on antibody only tests that may miss antibody only but 4 th gen would also test antigen and the likelihood of missing both multiple times is essentially zero?

Thank you
34 months ago
Sorry forgot to ask

4. If someone had the highest risk and tested with 4th gen lab based is 6 weeks enough knowing that no test is perfect? I myself as stated have tested out to 23.5 weeks  

Any reason for me to continue in this agony?

Thank you
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
34 months ago
Greetings. Dr. Hook invited me to add a comment.

I agree with all he said above about test reliability and performance. Most HIV exposures people ask about on this forum are very low risk, in which case even an imperfect test give highly reliable results. For example, if one's risk for HIV is 1 in a million and the test detects "only" 95% of infections, then after the test, the chance that person has HIV becomes 1 chance in 20 million. Even the most anxious persons should accept such a result as conclusive. (Stated another way, our advice on this topic is never dependent solely on the test result, even though that is usually the questioner's focus. We always take into account the combination of risk of exposure, whether symptoms are or are not typical for acute HIV, and the test itself. Never the test alone.)

For these reasons, for the entire history of this forum, we have from time to time advised persons at higher risk of HIV to not have the oral fluids test but a blood test, preferably a lab based (non rapid) test -- primarily because other tests are conclusive earlier, but also reflecting possibly a few false negative results even after 3+ months. So there is really nothing new in this topic. However, the real world performance of the test probably is better than 90-95% sensitivity. More likely it detects more like 98-99% of infections. Neither Dr. Hook nor I have ever seen any patient with negative oral fluids test who later turned out to have HIV. And to our knowledge, this also applies to all HIV/AIDS experts we know.
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34 months ago
Thank you both, but I had asked 4 specific questions in my last message, responses to those in particular my test out to 23.5 weeks with 4th gen lab based. Also had at 27, 42 and 14.5 weeks prior to 23.5. 

Thank you again
Edward W. Hook M.D.
Edward W. Hook M.D.
34 months ago
You need to be a little more patient.  I invited Dr. Handsfield to comment as well and neither of us attends to the Forum 24/7.  In answer to your specific questions:
1.  In most instances yes.  Certain ultra-high risk situations I might do something different but for virtually everyone more tests tend to strengthen the strength of results.  With two or even three negative tests, one should have complete confidence in the test result.

2.  No

3.  Combination HIV antigen/antibody tests have better performance characteristics than antibody only tests and therefore one should have greater confidence in the outcome of the combination tests than antibody only tests.  We do. 

4.  Yes.

Bottom line.  Your "agony" is misplaced.  Believe your test results and work to move on.  Please do not worry.  EWH
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34 months ago
Thank you Dr, not being inpatient and wasn’t  expecting an immediate response. 
I feel I am allowed one last set of question. 

1. So having 4th gen lab based tests at 27,42,69,102 and 182 days all negative more than enough for conclusive results? Blood draws from my arm. 

2. Would you recommend further testing for any reason?

I’m not irrational but definitely thinking irrationally. 

2. Would that be enough even with the highest possible exposure?

3. I don’t believe there is any better test I could have taken as I don’t want to continue this testing cycle.?

Sorry for acting repititive, apparent worry and anxiety. 

I am so done with worrying about this, it is affected my mood, etc and constantly fear my partner is infected (seems to get ill on and off) when I’m apparently not based on my results. 

FYI I did the tests via stdtestedpress which uses quest diagnostics. 

Thank you very much for helping. 
Edward W. Hook M.D.
Edward W. Hook M.D.
34 months ago
AS you acknowledge, some of these questions are repetitive.  Replies therefore will be brief.

1. So having 4th gen lab based tests at 27,42,69,102 and 182 days all negative more than enough for conclusive results? Blood draws from my arm. 
Absolutely.  Have confidence in these results.

2. Would you recommend further testing for any reason?
No unless there are future exposures.

2. Would that be enough even with the highest possible exposure?
Yes.

3. I don’t believe there is any better test I could have taken as I don’t want to continue this testing cycle.?
No

I hope these answers will let you move forward without continuing concern.  FYI, Quest diagnostics is a highly reliable, high quality, internationally respected laboratory.  As you reflect on your situation, I would urge you to consider what role guilt is playing on your concerns and if you feel that is contributing, work to either acknowledge and live with that guilt or address it directly.

That will be it for this thread.  Take care.  EWH
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