dna pcr test
Nov 27, 2010
Hi Dr. Bob,
I know that antibody testing is the "gold standard" of testing, but for who people who have a antibody producing deficiency would the HIV DNA PCR test be an acceptable test to use? I know that in some cases there may not be enough antibodies to make the antibody test accurate.
Last question, the DNA test is not FDA approved. Is this because of the cost and rate of false positives? What's the risk of a false negative with this test?
Response from Dr. Frascino
The only FDA-approved nucleic acid test is APTIMA-HIV-1 RNA qualitative assay. See below.
The problem with PCR assays is the rate of false positives, other technical considerations and cost. False negatives are generally not a problem with these types of testing assays.
APTIMA HIV-1 RNA QUALITATIVE ASSAY (APTIMA - HIV-1 RNA QUALITATIVE ASSAY, 2010) Nov 18, 2010
Dear Dr. Bob,
I thank you kindly and sincerely for your efforts, support and the invaluable knowledge you provide to the questioners on this forum. I have been reading this website extensively (over a month now) since my potential exposure date, and have been wavering as to whether or not I should post a question; at least certainly not before being as proactive as I can on my end with the tests currently available to me given the elapsed time. I wont even delve into what I believe to have been the onset and continuation of many ARS symptoms as I recognize actual test results always eclipse symptoms, many of which Im optimistically contributing to stress and anxiety.
My exposure risk, being a male, is unprotected insertive vaginal sex with a female stripper. The circumstances are tired, regrettable and the same; bachelor party, Im not much of a drinker, went back for what I thought would be a lap dance and left the establishment with dreaded horror. I have no way of knowing this womans HIV status or of getting in contact with her. Every day is a living nightmare now especially considering the questionable CDC per act risk of exposure guidelines in light of the Kimberly Powers North Carolina study.
So, seven days post exposure I went to my local Internist and got baseline tested for all STDs including HIV (ELISA). All test results came back negative although I know only Chlamydia and Gonorrhea would be reliable after such a short period of time. I was told to come back to test for HIV (and the remaining STDs) at six weeks, three months, six months and one year. Well, the anxiety has gotten the better of me
I just saw an Infectious Disease doctor (HIV Specialist) in the urban city in which I live. At 32 days post exposure, I took the Aptima HIV-1 RNA Qualitative Assay and just received the results, which were negative. I believe this is the only FDA approved test for diagnostic screening. Although Ive read your comments stating The problem with HIV PCRs is the rate of false-positive results and cost as well as 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.
Please correct me as this is purely supposition from what Im reading, but is the concern of using these tests for diagnostic purposes the high false positive rate, which would need to be confirmed with further testing; vice receiving a negative qualitative result after 28 daysor 32 days in my case, which some seem to deem conclusive? Or rather, it seems that negative test results for the Aptima HIV-1 RNA Qualitative Assay are potentially more reliable than positive results for diagnostic testing purposes, and Ive read on a few different websites that a negative test at 28 days is conclusive.
Can you kindly provide comment regarding this last paragraph? If nothing else, is this negative result an encouraging sign for me and/or are you able to assign an estimated percentage of the accuracy? The GEN-PROBE website cites a sensitivity confidence interval of 99.6%-100%.
Again, I thank you kindly for any response you can provide. If you would be so kind as to provide a link for donations in your response I will send one promptly.
All the best and continued good health and happiness. Signed, Aptimistaken???
Response from Dr. Frascino
Thanks for your kind comments! You are correct: the Aptima HIV-1 RNA Qualitative Assay is the only RNA PCR test approved by the FDA for HIV-diagnostic screening. You are also correct: the biggest problem with PCR assays is false-positive results and that is why a positive Aptima HIV-1 RNA test is considered a preliminary (unconfirmed) test result and requires a reactive (positive) "traditional" EIA (ELISA) HIV-antibody test before someone is given the diagnosis of HIV positive. False-negative results are not considered a significant problem with PCR assays. As for the exact window period for an Aptima test to be considered conclusive, yes, some Web sites and testing centers claim 28 days. I have not seen convincing scientific evidence that this is completely reliable. Confirming a definitive window period cutoff is extremely difficult, because there are a number of potentially confounding variables. Certainly we've learned from studying the natural history of HIV disease that those who have contracted the virus should have a positive HIV nucleic acid test by day 28. However, there are always unusual situations and rare complicating factors (such as technical or clerical errors) to consider. Nucleic acid testing is also much more difficult and costly to perform. All things considered, the HIV-antibody test taken outside the window period remains the gold standard for HIV diagnostic testing, at least for now.
PCR/nucleic acid testing can be very helpful in diagnosing acute HIV disease (ARS) within the window period. This is where I find the most appropriate use for this type of testing. I'll reprint below some information from the archives about the APTIMA test.
Donation information for The Robert James Frascino AIDS Foundation can be found on the foundation's Web site at www.concertedeffort.org. Thank you for your support. In return I'm sending my good-luck karma that you are now and will always be HIV free!
Be well. WOO-HOO on your negative APTIMA!
Another Aptima HIV PCR question Apr 19, 2010
Dr. Vegas here again. Thanks for the info re the Aptima PCR test. Could you answer another couple questions? When is the optimal time (to avoid false negatives) after exposure to do the test? I've been doing PCR's 4 weeks after exposure for both my occupational patients and those with sexual contacts. If the PCR is negative at whatever time is optimal what is the chance of the 3 month antibody test becoming positive? We do 3 month antibody tests on occupational exposures anyways but if the PCR is negative on the others is the 3 month antibody test still necessary?
Response from Dr. Frascino
Unfortunately there is no temporal relationship regarding the likelihood of obtaining a false-positive HIV plasma RNA PCR. The problem relates to the test sensitivity and assay methods rather than to anomalies in the plasma.
There have been no controlled studies to scientifically answer your question concerning an undetectable PCR RNA at a specific time followed by a reactive anti-HIV antibody test at a later date. The anti-HIV antibody test at three months remains the gold standard. The Aptima PCR test is FDA approved for diagnosis, and other quantitative HIV PCR RNA tests and qualitative HIV PCR DNA tests have been used to identify infected patients during the acute retroviral syndrome. If a four-week Aptima PCR is undetectable, it would be extremely extremely unlikely a three-month HIV antibody test would be reactive in my experience.
Role of HIV PCR (APTIMA HIV-1 RNA QUALITATIVE ASSAY FDA APPROVED FOR DIAGNOSTIC USE) Apr 14, 2010
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 . . . .
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
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