question about a certain test they do in British Columbia (NAT TESTING)
May 24, 2009
First off i'd like to commend you on the great work your doing and the patience you have for all the questions you get and answering them in a comical manner on a non comical issue, I really do admire you. I have a question about some tests that i took after a protected/non condom breaking/lady of the night from Thailand episode. I went and got tested at the 7 week mark. I was negative on both an ELISA test and a new test they are offering to only men called a POOLED NAT? Do you know anything about this test? is it offered in the USA? I took it at the British Columbia Center for disease control head clinic in Vancouver and they told me it was a 98% accurate. Is that possible? as i've read on here many times nothing is that accurate until the 3 month mark...anywho thank you for your time, and thank you very much if you can get back tome on this. A donation is in the works.
Response from Dr. Frascino
NAT stands for nucleic acid test. (NAAT, nucleic acid amplification test, is another notation for the identical test.) It is a qualitative test that screens for very small amounts of HIV (or other pathogens such as hepatitis C) genetic material (DNA or RNA). The process, called amplification, involves a fully automated way of massively copying (amplifying) the viral genetic material so that it can be detected and identified. The "pooled" part of the test indicates that the test is performed on pooled samples. Usually about 20 individual samples are mixed together and tested as a batch. If the batch tests positive, then each of the 20 individual samples is tested individually (using the usual serological testing methods). NAT is expensive, which is why it's run as a pooled batch. NAT has been approved by the FDA in the U.S. for use in screening donated blood. In laboratory studies NAT reduced the HIV window to 12 days. Its use outside the approved blood-donor-screening indication is being evaluated. Is it 98% accurate at seven weeks? It's possible, however, I don't believe we have sufficient epidemiological data to make a definitive claim. Also, 98% would still miss 2 out of every 100 tests. At this point I would continue to defer to the guidelines and recommend an HIV-antibody test at the three-month mark as the gold standard. I'll repost below some information about NAT testing in the U.S.
Certainly your negative ELISA and NAT at seven weeks following your P/NCB/LOTNFTE (protected/non-condom breaking/lady of the night from Thailand episode) is extremely encouraging. The odds are astronomically in your favor that your one night in Bangkok banging cock (protected!) did not result in HIV transmission.
Thank you for your donation to the Robert James Frascino AIDS Foundation (www.concertedeffort.org). In return I'm sending you my good-luck karma that your definitive three-month test remains negative. I'm confident it will.
Continue to play safe and you'll stay safe.
Was I misinformed??? (NAT TESTING 2008) Aug 1, 2008
Hey Dr. Bob, I'll be brief. I recently donated blood and requested to come in and pick up my results. Everything came back negative and the Director of the Lab told me that they use the HIV antibody test as well as the HIV NAT to screen donated blood. She said that the HIV NAT picks up infection anywhere from 10-15 days past acquiring the virus. Do you know if this is true or not? I donated blood 18 days past my last sexual encounter. Would the HIV NAT have picked up infection by then? I was just wondering if what the woman at the lab told me was true. Thanks and keep up the GREAT work!
Response from Dr. Frascino
Please note that the purpose of the testing done at blood donation sites is to protect the blood supply, not diagnose HIV infection. NAT testing can pick up some HIV infections prior to standard HIV-antibody tests. (See below.) I certainly hope you were not using the blood donation service as a means of checking your HIV status after your sexual encounter 18 days ago. If you had any worry whatsoever that you might be HIV infected, you would not have donated blood, right?
NAT Testing Apr 26, 2008
I had a possible exposure to HIV on or around March 19. I made a major mistake by having unprotected sex with a stranger. He later told me he was HIV positive and has since changed his cell phone number, so I was unable to confirm if he was indeed positive nor was I able to get further information about viral load etc.
I waited until April 3rd to get tested. I live in Los Angeles and was fortunate enough to receive free NAT testing. Additionally, I was screened for all STDs. Everything came back negative. The counselor said that I am 100% negative as of March 13 (before the possible exposure) and assured me that I should feel confident about my negative result being conclusive. My question is how good should I feel about the 15 days I waited before getting the NAT test? Do you have any statistics around how long it takes for the virus to present itself?
Response from Dr. Frascino
The current testing guidelines still recommend HIV-antibody testing at the three-month mark. Other more sensitive tests are being developed and coming online; however, the formal guidelines have not yet been revised, as we are still gaining information about the sensitivity and specificity of the newer tests. NAT allows us to detect very small amounts of genetic material (DNA or RNA) via a process called amplification, which involves massive copying. In laboratory studies NAT testing reduced the time to viral detection to 12 days. So is your 15-day negative NAT WOO-HOOable? Honestly I don't know. There has not been enough published research for me to make that a definitive statement. I'd still recommend the 3 month antibody test.
NAT test Aug 5, 2007
Dr. Bob, some states actually use a nat test along with an antibody test to check subjects for hiv. They take two viles of blood for this. Can you tell me what a nat test checks for ?
Response from Dr. Frascino
Sure. See below.
nucleic acid testing May 16, 2006
dr. bob, i'm a 25 year old guy who made a mistake and had brief unprotected insertive anal sex about 5 weeks ago. The guy also had his penis around my anus- but not in. Of course, I'm beating myself up and my anxiety is really kicking up right now. I had an hiv test and std screenings at one week. All negative/non reactive. My anxiety got very bad and my dr. recommended having a nucleic acid test at 3 weeks if that was the case. I found a program at the los angeles gay and lesbian center that offers free diagnostic nat for hiv. I went about 10 days ago and get the results tomorrow. I know you don't recommend this as a means of diagnosis, but I wanted to know what you know of the testing they offer and whether or not it is reliable. also, is the chance for a false positive still high as i believe it is a pooled nat test?
whether or not you answer this, thanks for all your help and support, you've gotten me through a scare once before and hopefully i'm a day away from woohooing again. or at least a woo. you really are an angel.
Response from Dr. Frascino
Yes, I am aware the Gay and Lesbian Center in Los Angeles began offering free nucleic acid amplification testing (NAT). I believe they are the first site in Los Angeles County to do so! By report, this testing assay, which detects actual HIV rather than antibodies to the virus, can give accurate results within three to four weeks, compared to three months for standard HIV-antibody tests, such as ELISA. I do not have specific information about the rate of false-negatives or false-positives for the specific testing assay the center is using. However, chances are the folks at the center would be able to provide you with whatever information has been generated so far. I do believe the general testing assay (NAT) is indeed valid. More information should be available fairly soon if this type of testing becomes more widespread and available. I'll try to keep you posted as reliable information evolves.
Three New Assays Approved
May 25, 2007
On May 23, 2007, FDA approved the Procleix Ultrio Assay on the fully automated Procleix TIGRIS system manufactured by Gen-Probe Inc., of San Diego, California, and marketed by Chiron Corporation. This is a fully automated qualitative in vitro nucleic acid test (NAT) to screen for human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) RNA in donated blood from donors of whole blood, blood components, or source plasma. It is also licensed to screen individual organ donations from living donors, heart-beating organ donors, and cadaveric (non-heart-beating) organ donors. The capability of full automation will reduce human error and accelerate blood screening, enhancing blood safety.
On May 11, 2007, FDA granted marketing approval to two HIV-1 PCR assays for use in managing the treatment HIV infection.
The Abbott RealTime HIV-1 Assay, made by ABBOTT Molecular, Inc., is an in vitro reverse transcription-polymerase chain reaction (RT-PCR) assay for the quantitation of Human Immunodeficiency Virus type 1 (HIV-1) on the automated m2000 System in human plasma from HIV-1 infected individuals over the range of 40 to 10,000,000 copies/mL. The Abbott RealTime HIV-1 assay is intended for use in conjunction with clinical presentation and other laboratory markers for disease prognosis and for use as an aid in assessing viral response to antiretroviral treatment as measured by changes in plasma HIV-1 RNA levels. (Product label)
The COBAS AmpliPrep/COBAS TaqMan HIV-1 Test, made by Roche Diagnostics is an automated PCR test, indicated for the quantitation of Human Immunodeficiency Virus Type 1 (HIV-1) nucleic acid in human plasma (viral load) for use in conjunction with clinical presentation and other laboratory markers. The test is intended for use in conjunction with clinical presentation and other laboratory markers of disease progress for the clinical management of HIV-1 infected patients. It can be used to assess patient prognosis by measuring the baseline HIV-1 RNA level or to monitor the effects of antiretroviral therapy by measuring changes in plasma HIV-1 RNA levels during the course of antiretroviral treatment. (Product label)
Neither the Abbott RealTime nor the COBAS AmpliPrep/COBAS TaqMan HIV-1 assay is intended to be used as a donor screening test for HIV-1 or as a diagnostic test to confirm the presence of HIV-1 infection.
blood donation and notification May 18, 2006
Hey doc, Just wanted to say before i ask my question, that you provide a wonderful service and should be commended for your expertise and sacrifice. My question is this: About two weeks ago, i donated blood. I dont consider myself at risk, and i answered all questions honestly. Anyway, the other day, i called the blood bank to see if and when i could donate again. The woman on the phone gave me a date and the conversation ended. (I must admit that i had two motives in makeing this call. I would like to donate again, but i also wanted to know the status of my blood) Would the womans prompt response of my eligibility date mean that my blood has been approved for use?(I gave her my blood number, name, and date of birth) Finally, if my blood tested positive for anything, how long would it be until i was contacted about it? Lastly, how would the red cross notify me of any possible condition? (mail, telephone, etc.) Thank you for all of your help in this matter.
Response from Dr. Frascino
If you don't consider yourself at risk and answered all the questions honestly, I don't understand why you had a second motive for your call.
If, on the other hand, you have cause to be even slightly concerned that you may be HIV positive and decided to give blood anyway because you "wanted to know the status of my blood," that is unconscionable and immoral and you should be ashamed of yourself. Since I strongly hope this is not the case, I'll simply advise you that since you do not consider yourself at risk and answered all the questions honestly, you have absolutely nothing to worry about. Right?
NAT is FDA-approved only for use in screening donated blood. It is not approved for routine HIV screening for individual patients. There are a number of reasons for this having to do with the sensitivity/specificity of the testing assay and the cost. The purpose of blood-donation screening is to protect the blood supply. Consequently the sensitivity of the screening tests is set so that it will err on the side of protecting the blood supply. In other words, if the test picks up some false positives, no problem. The questionably positive blood can then be discarded. Donors are notified to follow up with their doctors to see if their test was a false positive or if they are truly HIV infected. Again the primary purpose of these tests is not to diagnose patients, but to protect the blood supply. NAT is also extremely expensive. NAT testing is performed on pooled samples. That means usually around 20 donor samples are mixed together and tested as a batch. If the batch tests positive, then each of the 20 donor samples is tested individually by our usual serological testing methods. See, I told you this was a bit confusing.
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