HIV testing results

[mark26]

Dear Dr. Handsfield

Thank you so very much for all your wonderful work and such a dediacted site.

I gave a man oral for literally a few seconds and was tested (duo ab/ag) after 4 weeks.  I was shown the result sheet which was negative.  However, I've been puzzled about the actual reading from the test which was 0.27.  I also remember seeing something that said <0.9 (like an index value!).  

Could it be that I had just not reached the threshold for positive result because it was too early and the 0.27 value will go up by the time it's been 12 weeks?

I guess what I'm trying to ask is that why was the reading not zero? Could it be that here in UK they set their threshold value for what would be considered high enough after 12 weeks so after 4 weeks even if you have some detectable ab or ag, the result would be negatine nonetheless.

I know the theme has been repeated in the forum but it's just that they seem to be really fussy about the 12 week thing in this country.

Thanks for your help in advance

[jadeorchid]

A related discussion, home acess and hiv at 4 weeks was started.

[WorriedUS]

I read another post from the Doc that says antibodies don't interfere with testing for antibodies for HIV.  Do a search for "antibiotics HIV" or somethin like that.

[lizmik]

Hello, two weeks after unsafe sex, I took an Elisa test which included testing for P24 antigens, which are usually only ascertainable 1 to 3 weeks after exposure. The results came back negative. However, at the same time, I was taking 3 different kinds of antibiotics for a bladder infection. I was wondering if anyone knows if antibiotics can alter results for HIV testing? I do intend to test again after three months to check for antibodies. Looking forward to any comments and help I can get.

[Ronnie99]

Figure 1 is confusing to me due to the labeling of the graph. What is being measured on the verticle axis? Is it the percentage of people who test positive with the given test at the number of days shown on the horizontle? If so, the Elisa looks like it sill has a ways to go at 12-13 weeks post exposure.....

[skerdstraght68]

take a look at this.  It will back what the doc says.  Figure seven is a good graphic showing time to test.  It says on the bottom that time to show on an elisa is 3-4 weeks.  

http://depts.washington.edu/hivaids/initial/case1/discussion.html

[skerdstraght68]

and one more thing, I called the lab in my city and it appears that the latest elisa test indeed uses the p24 and Antibody test. (AKA Duo).  It would seem that even if you were a little early the p24 antigen test would more than likely pick up that actual virus and if you were past that stage the antibodies would be picked up by the elisa.  She informed me the new tests are very sensitive at 4 weeks.

[Ronnie99]

I am somewhat confused as to how a quarter of the population of some African countries can be infected with HIV if the virus is extremely difficult to catch.

[H. Hunter Handsfield, M.D.]

That question has been addressed, although not for several months.  Search older archives for "HIV transmission risk".  The answer has to do with stage of the epidemic, which in turn affects the proportion of recently infected people with high viral loads; lack of antiviral treatment; and background rates of transmission cofactors like circumcision, other STDs, and certain sexual practices (such as "dry sex"); and others.

No prolonged discussion, please; it's a thread jump.

HHH, MD

[Willl]

http://www.newsrx.com/newsletters/Vaccine-Weekly/2006-05-10/051020063332VW.html

[skerdstraght68]

Doc, can you look at what I posted specifically graph 7 and tell me if "stage" = weeks?  It appears some of the data is comprised from Seattle.

[Willl]

It is not meant to be weeks, see figure 1

http://www.retroconference.org/2001/posters/415.pdf

[H. Hunter Handsfield, M.D.]

jacobsquestion is right.  Your risk probably was well under 1 in in 10,000 which applies to more prolonged oral exposure than "literally a few seconds".  Calculate the risk:  For sake of argument, let's say there's a 10% risk your partner had HIV; if he did, 1 chance in 100,000 of cathing it; and a 10% chance your 4 week test missed the infection.  Your odds of having HIV are 0.1 x 0.000001 x 0.1 = 0.0000001.  That's one chance in 10 million.  Even if you know your partner was infected and if you assume the highest possible risk of transmission (1 in 10,000), the risk calculates as 1 in 100,000.  These odds are less than the chance you will die of some accident or unexpected illness in the coming week or so.

So put things in perspective.  Have 9 and/or 12 week tests if you like (definitely not both!), but don't lose any sleep over it in the meantime.

HHH, MD

[Willl]

No, the vertical axis is the progression of markers of HIV infection. I think you are looking at the "LS-AB" (less sensitive antibody).

[Ronnie99]

But the increasing green line (Elisa/EIA) for example means that the proportion of people testing positive using Elisa is continually growing, right? From days 25 to 30 or so the percentage of people that will test positive is growing very fast, but then levels off..... Unless I'm missing something this shows also that the p24 test is relatively accurate early on but then the proportion of people testing positive falls off over time. I'm not sure what the falling RNA number means... Is that because for some people the viral load falls to an undetectable as their body initially contains the infection?

What I meant originally was I did not understand why there is no scale on the verticle axis.

[Willl]

You are trying to correlate an estimated graph of antibody rise to percentage of people testing positive and there is not a 1 to 1 correlation here, but it should be a close estimate. The p24 drops as antibody increases because your body is fighting off the virus. Some tests are not worth taking after a certain amount of time has passed.  

{for an example of a marker, the more we post about this the more I forsee this being deleted by Dr. H as a thread jump).

The most accepted standard is still the good old ELISA that you have to wait around for.

[Willl]

"On the basis of a presumed 22-day window period to the detection of HIV antibodies by IgM-sensitive EIA, and approximately 5 days each for the two preantibody stages characterized in this study, we have derived estimates of the marker-negative, potentially infectious window periods for p24 antigen and HIV RNA of approximately 17 and 12 days, respectively."

"The less sensitive second-generation EIA became reactive on average one week after the IgM-sensitive EIA"



http://www.aidsonline.com/pt/re/aids/fulltext.00002030-200309050-00005.htm;jsessionid=GJvG7wNjhM41tL2LV68B1TJGFSpb8NG3qlyqmDhpSyQl0CK7W9zh!1941873617!-949856145!8091!-1#FF1

[skerdstraght68]

So does that mean that when the virus becomes unreadable by p24 antigen, there are detectable amounts of antibodys for the EIA to pick up?

[skerdstraght68]

"Window period closure for p24 antigen relative to HIV-EIA antibody was based on an average duration of 5 days from p24 antigen to IgM-sensitive EIA reactivity in this study"

It appears there is a point in which the P24 is non reactive as well as the EIA

[Ronnie99]

Too bad they did not include the pcr proviral DNA test on there. That is the one I took... lol

[jacobsquestion]

You had an extremely low risk to begin with - I don't even think testing was needed.   you have a 1 in 10,000 chance of getting HIV from giving oral.

[mark26]

Dear Dr. Hansfield

Thanks vey much for your reply.  Do you mean that I can relax about the results?

I'm planning to have a 9 week test and a 12 week one as well.  Can't help but worry about this since there seems to be so much controvercy around oral sex and reliable testing time.

Thanks very much again.  I really appreciate your help.

Mark

[H. Hunter Handsfield, M.D.]

The reason the test result is not zero has to do with the chemistry of the test, not detection of "a little bit" of antibody.  Any test value below the positive threshold is a true negative in every sense; there is no difference between a value of, say, 0.1, 0.3, or 0.8.  Your result is absolutely negative.  I'm sure UK labs do not set the threshold differently than anywhere else; insistance on 12 weeks for definitive testing is simply a conservative approach, not because of different test methods.

The chance you have HIV, with the negative test result at 4 weeks, is astronomically low.  Best wishes--  HHH, MD