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PCR Questions related to PEP

May 25, 2010

Hi Dr. Bob, some more questions for you from "such an idiot"!

1. How effective is the PCR test at determining HIV status? I guess more specifically, how much earlier than standard antibody tests can PCR give an answer, and at what confidence level?

2. Does using PEP affect the time frame for effectiveness of the PCR test? In other words, does the timeline of uncertainty extend out farther because I'm doing PEP?

Thanks so much, and I truly appreciate your time. I am forwarding another donation at this time.

All the best!


Response from Dr. Frascino

Hi Mr. Idiot,

Welcome back to the forum.

Only one HIV PCR is FDA approved for HIV-diagnostic screening. See below.

HIV RNA PCR testing should not be used for HIV-diagnostic screening while you are on PEP, as it can lead to a "false negative" result. (See below.) The post-PEP testing guidelines recommend an HIV-antibody test at six weeks, three months and six months from the date of exposure.

Dr. Bob


I am a family physician and first I wanted to commend your frank and frequently humorous answers to your readers questions. The appropriate use of humor when taking care of patients humanizes us as physicians. Continue your good work.

I am the medical director of a Las Vegas occupational/urgent care medicine clinic. We frequently see and manage blood borne pathogen exposures. (as well as the occasional patient who did something in Vegas that they want to stay in Vegas) Most are exceedingly low risk for HIV (needle sticks from diabetes syringes left in trash, etc) Some are slightly higher risk (HIV patients as source). Hepatitis B is a bigger concern but thanks to vaccine it doesn't present a huge problem.

In cases where the risk is slightly higher or the patient is exceptionally anxious I have been doing a 4 week HIV PCR. Our local Quest lab says this test is greater than 95% sensitive at 4 weeks. There are of course different PCR's. Judging from some of your answers it appears you don't recommend them. I agree that the 3 month HIV antibody test is definitive and seals the deal. Is there any role for the PCR's in my setting?

Response from Dr. Frascino


Medical director of an urgent care facility in Vegas??? Now that must really be an entertaining position. I love Vegas and visit frequently. I'm always amazed at the often bizarre-appearing folks I see lumbering in and out of casinos on The Strip. I often have the urge to walk up to some of them and just say, "I demand an explanation." But, I digress . . . .

The problem with HIV PCRs is the rate of false-positive results and cost. Only one HIV-1 RNA PCR test is FDA approved for diagnostic screening (so far). It's the Gen-Probe APTIMA assay. (See below.)

Other HIV PCR tests are sometimes used to help diagnose someone who presents with a history of significant HIV exposure and is developing acute retroviral syndrome symptoms while still within the window period (defined as the first three months after exposure).

Hope that helps. Now can you help me with my craps game? I'm still a bit uncertain about all those onetime bets in the center of the table.

Be well. Thanks for appreciating my admittedly twisted sense of humor. Then again, you do live in Vegas, so . . . .

Dr. Bob

Approval of HIV-1 RNA qualitative assay for diagnostic use

The Food and Drug Administration (FDA) announced the approval, on October 5, 2006, of the APTIMA(r) HIV-1 RNA Qualitative Assay, manufactured by Gen-Probe Incorporated of San Diego, California, for use in clinical laboratories and public health facilities to detect primary (early) HIV-1 infection. The APTIMA® HIV-I RNA Qualitative Assay is an in vitro nucleic acid test (NAT) for the detection of human immunodeficiency virus (HIV-1) in human plasma intended for use as an aid in the diagnosis of HIV-I infection, including acute or primary infection, before the appearance of antibodies to HIV-1. Traditional detection and diagnosis of HIV-I infection is based on testing for anti-viral antibodies by enzyme immunoassay (EIA) with confirmation by supplemental antibody tests such as Western blot or immunofluorescence assays (IFA). Although sensitivity of HIV-1 antibody detection has increased in the last few years, a window period between infection and detectable serological markers still exists. Following a recent exposure to HIV-I, it may take several months for the antibody response to reach detectable levels, during which time, testing for antibodies to HIV-I, including the use of rapid antibody tests, will not indicate true infection status. The newly approved test may provide earlier diagnosis of infection because it detects nucleic acid of the human immunodeficiency virus (HIV-1) in human plasma, rather than the antibody response to the virus. Presence of HIV-I RNA in the plasma of patients without antibodies to HIV-I is indicative of acute or primary HIV-1 infection. The test, however, is not meant to be used as a stand-alone test for the diagnosis of HIV-1 infection. A positive nucleic acid test should be viewed as a unconfirmed test result, indicating probable infection, and should be followed up later with traditional EIA antibody testing to confirm infection with the Human Immunodeficiency Virus. In addition, the APTIMA HIV-1 RNA Qualitative Assay may be used as an additional test to confirm HIV-I infection in an individual whose specimen is repeatedly reactive for HIV-1 antibodies. This is important because the Western blot can, in some instances, be difficult to interpret and may not always provide a conclusive result. The APTIMA test can be used instead of the traditional Western blot test or IFA for confirmation of HIV-1 infection when the screening test result for HIV-1 antibodies is positive. The sensitivity of the APTIMA(r) HIV-1 RNA Qualitative Assay is comparable to that of FDA approved viral load assays that measure the amount of HIV-1 virus circulating in the blood of patients with established HIV-1 infection to monitor the treatment and progression of AIDS. Unlike the viral load tests, however, the APTIMA test has been approved for the diagnosis of primary HIV-1 infection, as well as for confirming HIV-1 infection when tests for antibodies to HIV-1 are positive. The product labeling for this test will be available soon on the list of FDA Licensed/Approved HIV, HTLV and Hepatitis Tests on the FDA web site. Richard Klein Office of Special Health Issues Food and Drug Administration

What do you think about this? Apr 28, 2010

Hi Doc,

I am 20 years old and currently on PEP medications. I found out that my partner (17 years old) is HIV+ on the 19th of this month. We had fucked numerous times (a dozen times I would say) bareback... I was always the top in this scenario but obviously this is very high risk. We used KY most of the time, but one time only used his saliva as a lube. This was the last time that we did anything and was within 24 hours of my start on PEP. What are the chances that I got HIV? I am cut, he is uncut... the only 2 times he fucked me involved using a condom and he only came once inside that condom that was inside me. I feel so stupid and I partially blame Celexa - the anti-anxiety medication I was on when all this occurred. There was never blood seen when I fucked him but there was anal leakage, possibly lube too that came out of his ass. I did not have any noticeable cuts or anything on my dick. I believe he became infected in December so I am unsure of how high a count he would of had. I did notice that he had very large tonsils =( I can't believe this is happening to me, I am too young and I don't want to die because of something like this. Can you offer any advice? I was tested for Syphillis and it was negative but I had previously chlamydia in January. Maybe that makes a difference Idk. When can I have a definitive test result? My Drs. ran an RNA viral load test 4 days after the last exposure and we are still waiting the results. Would a clear test mean I am ok? We started having sex on the 14th, I began treatment on the 19th...

Response from Dr. Frascino


No doubt barebacking is risky business and I don't think you can blame it on Celexa! You consciously and deliberately ignored my two cardinal rules for HIV prevention:

Cardinal Rule #1: Assume all your sex partners could be HIV infected and take all the necessary precautions to prevent transmissions of the virus.

Cardinal Rule #2: Always remember Cardinal Rule #1.

PEP may offer some degree of protection from your last exposure, as it was started within 24 hours. It would not provide protection for exposures that took place more than 72 hours prior to the time of your first PEP dose.

Regarding HIV diagnostic testing, the published guidelines for post-PEP HIV screening recommend an HIV-antibody test at six weeks, three months and six months from the time of your last HIV exposure.

HIV RNA PCR testing while on PEP for diagnostic purposes is not advisable. You could be HIV infected and your PEP medications, which are comprised of antiretrovirals, could theoretically be driving your HIV plasma viral load to undetectable levels. Consequently an undetectable RNA PCR used for diagnosis while on PEP may yield a "false negative" result in someone who is HIV infected.

Finally your comment -- "I can't believe this is happening to me, I am too young and I don't want to die because of something like this." Please note these exact sentiments apply to each and every one of the over 33,000,000 of us cohabitating with HIV.

I do sincerely hope that you have not acquired the virus. I'm confident this entire anxiety-inducing experience has served as a wakeup call that barebacking is not worth the potentially catastrophic consequences. Your story should also serve as a cautionary tale for all those reading this forum.

Good luck. I'm here if you need me, OK? We'll get through this together, whatever the tests show.

Dr. Bob

Anal Rape
Protected Top/ Chlamydia/ HIV poz bottom

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