Question:

I was just wondering if you could tell me how accurate PCR DNA tests are in finding the HIV virus in people? I had one done at thirteen weeks after unprotected sex as well as an orasure test and they both were neg. I am wondering if I was infected should the PCR have picked it up?? Also what is the difference between a PCR DNA and a PCR RNA?? Some one had told me that if I was infected and the virus had calmed down in my body that the pcr would not have picked it up?? Is this true or is the virus always there and the PCR DNA would pick it up but the PCR RNA wouldn't??

Answer provided by:

Peter Shalit, M.D.
Internal Medicine

DNA tests are very accurate even very early in HIV infection. At thirteen weeks both the RNA and the DNA test should be positive if you are infected. The difference between the two is that DNA tests for the virus that is living in the cells, while RNA tests for the virus that has been released from the cells and is in your bloodstream. Theoretically, it is possible for a person to have such a low grade HIV infection that their RNA test is "negative", which means that there is less RNA than the test can detect. In these people, the DNA test would still be positive.

I asked a colleague for help with your question. Janine Maenza, MD, runs the Primary HIV Infection Clinic at the University of Washington. In addition to confirming what I said just above, Dr. Maenza wondered why the DNA test was performed, since it is rarely done outside of a research setting, and since the RNA should be positive at 13 weeks. She felt that a DNA test might be more useful in the first few weeks after infection, if the antibody test is negative and the RNA test is low or equivocal.

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