Polymerase chain reaction (PCR) test

[lexman]

I am thinking getting this Quantitative Polymerase Chain Reaction (PCR)HIV test, it is expansive but they say can give you a 98-99% answer even within 72 hours after possible exposure. But recommended to wait at least 14 days for more accuracy.

[winza]

what do they mean by a false positive? is there a false negative?

[Xhost]

Hi,

Of course, anyone may have any test that they choose. It really is up to the individual. I believe what I wrote would apply to RNA or DNA tests (actually, I am not certain what the differences may be, so maybe I should just shut up about that).

Look, I know how it feels to be sweating out a 6 week antibody test. I've walked that mile in those exact shoes, and I gave in to the temptation to have the PCR. Twice. People made the same arguments that I have made against them to me, and I didn't listen. OK, it worked out for me, as it will work out for other people. The problem is the people who get the false positive.

To me, the chance that I might get one was abstract. After I got my tests, I wondered what all the fuss was about. And I continued to wonder until I met the person who I described in my original post. Then I understood - aha! This was why people do not recommend these tests for diagnostic purposes for persons in low risk categories.

I can see the validity in someone having this test when they've had a high risk exposure. A baby born to an HIV positive mother, unprotected anal or vaginal sex with someone known to be HIV positive, a needle stick in a clinical setting.

But, for most of the posters who come here, well, they are not so high risk. In many cases, they were in the no or very, very, very low risk category. For these people, it really makes no sense to shell out the 300 smackers for a test that they don't need, and which also may ruin their lives for some period of time.

Most of the people here are as skittish as a horse in a barn fire when it comes to HIV. As such, what do you think a false positive is going to do to them if they are unlucky enough to have it happen to them? Nothing good.

I'm not a doctor, and I am not a test expert. Anyone is free to disagree with what I am saying. In fact, I welcome the discussion, because if I am giving bad advice, I want to know it so I can stop doing it. In this case, though, I am not sure I am. Of course, people are free to disregard, and just go ahead and get the test. I can't blame them for doing it, because I did it myself. I only hope to offer advice based on my own experiences, and show the possible pitfalls in taking a PCR test.

[OralMistake]

xhost, I am wondering, and I write this with all due respect, if what you write applies to both DNA and RNA tests. I think the RNA which is the qualitative PCR as opposed to the quantitative test and is used, for example, to screen blood donors, is a valid test after 12 days. Eventhough it's not recommended (high costs, false positives) I submit it's still a valid test.

[Xhost]

Hi Lexman,

I think what the first poster was alluding to was why do you think you may have been infected with HIV? Typically, for 99% of the posters that post here everyday, the risk of catching HIV is not really very realistic at all.

Which brings me to my next point. Any PCR test that you may be thinking of taking was not designed to be a diagnostic test. It was designed to do viral load counts on those already confirmed to have HIV. Many doctors (including the one on this site) would, in almost all cases, recommend against taking one. Also, the FDA has not approved PCR as a diagnostic test.

One of the main drawbacks of the PCR is that it will, on occasion (with far too much frequency), report that a negative person has some x number of viral particles per ml in his or her blood. For someone already anxious about HIV, this can be devastating news. I know this because I have spoken to someone here who was in just that circumstance. This person went through a hell of a time, and was scared to death. Turned out, after weeks of worry and depression, this person eventually wound up testing negative on a standard antibody test. Happiness and merriment ensued, but those few weeks of worry were hell.

A couple of other points:

--There is no official window period for a PCR test. It wasn't meant to be used as an HIV test in the first place.
--Any testing company that sells you this test will also tell you to follow up at 13 weeks with a standard antibody test, because the antibody test is the only sure way to know anything in terms of HIV status. This begs the question why they offer the test in the first place, but there you have it. Given this point, it makes more sense to wait for a (in most cases) definitive 6 week test.
--Most testing front companies will tell you that a PCR test result is really only "valid", or definitive, after 28 days. Which means that, if you can hold on for 2 more weeks, you can go in and get an antibody done that will cost you much less and have much less risk of giving you a false positive.

In the interests of full disclosure, when I was sweating out the window period, I went and had two PCR tests. Luckily, they both came back negative. At the time, people tried to warn me not to have the PCR, indicating that it was a waste of money. I wouldn't listen, though, because I just had to know right away.

Thing was, even after my two tests (done at 14 and 28 days), I read online that the PCR does not provide a definitive diagnosis. So, still wound up getting a later antibody test. I look back on the money I spent on the tests and wish I had it back. Plus, had I been unlucky enough to receive a false positive, I may just have jumped out of a window.

I know it's hard to think about waiting. But, that's one of the good things about this site - you can sweat it out in company, which you may find comforting. Just remember, you aren't alone, you can always reach out here and people will be jumping all over themselves to provide you any help they can.

Good luck to you.

[OralMistake]

Hi, window perior for PCR RNA is around 12 days.

Regards.

[lexman]

rob73-thanks for all that info.

my possible exposure was a week ago.

[Rob73!]

Lex, you need to know that PCR test does have a higher instance of false positive results than other HIV tests. I'm not sure of the time post expsoure when it can detect HIV. My advice to you would be to not have the PCR test (i'm guessing your stress and anxiety levels are going through the roof?) and wait until 28 days post epxosure and have an HIV DUO test, which uses the ELISA assay AND looks for the P24 protien marker. This test is a better bet all round as it almost never produces false positives.

Remember most people will develop detectable HIV antibodies between 21-26 days so any test taken after about a month will give you an accurate result.

BTW you don't mention your possible expsoure. None of our business, but the majority of posters on this forum are very knowledgeable about potential expsoures and would, I'm sure, give you better advice than I.

Good luck!