|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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