RNA testing in conjunction with HIV test
Jul 31, 2008
Hello Dr. Bob,
I would really appreciate it if you could help me. I have had tests done at six and weeks post possible exposure for HIV. Both tests are negative. I understand this window is more definitive at 12 weeks. However, I also had an RNA test done at 7 weeks which came back with the virus being "undetectable". While I still plan on having an HIV test done at 12 weeks, can I consider the results of the RNA test essentially a confirmation that I am negative, or is the 12 week test really the confirmation that I need?
Very grateful if you could let me know. Thank you.
Response from Dr. Frascino
Your "undetectable" quantitative RNA plasma viral load test is very encouraging. However, PCR RNA tests are not recommended for routine HIV screening. (See below.)
why don't you ever recommend the RNA tests? Jul 31, 2008
Dear Dr Frascino, Thanks for answering my previous question. When I'm not so poor, I will make a donation to your fantastic organisation. My question to you is simply this: why do you only ever recommend the HIV antibody test (which necessitates a 3 month wait post-exposure)? I've been tested several times here in San Francisco and they have always given me the new RNA test - which they tell me can detect the virus with 100% accuracy only 10 days post-exposure. Is this because you think the RNA test is less accurate than the traditional antibody test, or is it the case that this test is not available countrywide and you want to recommend a test everyone can obtain access to?
Response from Dr. Frascino
Thanks for your question. It's one that comes up quite often. There are several reasons for recommending HIV-antibody tests over RNA-PCR tests for diagnostic purposes.
1. HIV-antibody tests are FDA approved for diagnosing HIV disease. PCR tests (RNA and DNA) are not. Large epidemiological studies have been conducted to verify validity, sensitivity and specificity of HIV-antibody tests. The false-negative/false-positive percentage is acceptably low, particularly when combining a Western Blot test for confirmation of positive ELISA/EIA/rapid tests.
2. PCR-RNA has a risk of false-positive results. Getting a false-positive result when screening for a condition as catastrophic as HIV can lead to significant anxiety. Just check the archives for a number of testimonials that provide concrete examples of this. (Or, just imagine if it happened to you!) RNA tests were not designed (or approved) for routine HIV screening and diagnosis. HIV PCR RNA tests are used to monitor how much HIV is growing (how rapidly HIV is replicating). It is very possible to be HIV infected but have an "undetectable" PCR-RNA if someone is on antiretroviral therapy (PEP, for instance). This could lead to confusion: The person tested might think he is HIV negative when in reality he is HIV positive but at the same time RNA undetectable.
3. Availability and cost. PCR-RNA testing is very costly and not available worldwide. My comments on this site are read throughout the cyber-universe.
Finally, I should mention I recommend quantitative PCR RNA and qualitative PCR DNA tests. Lots of them! However, I recommend them for specific purposes and routine HIV screening is not one of them.
Hope that helps.
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