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Should I get a PCR test?
Oct 14, 2007

Hi Dr. Bob, Thank goodness for you and your patience. Your forum is a much appreciated venue for reliable information. I had unprotected receptive anal sex 4 weeks ago. It was with an anonymous partner who didn't ejaculate in me. Over the past two weeks I have been experiencing a range of symptoms that indicate some type of infection. I.e. - upper body rash, fever on and off, occasional chills, and a pretty relentless sore throat. I visited a (obviously homophobic) Doctor who told me he was convinced I was seroconverting and ordered a PCR test. I opted for an Oraquick antibody test (I know it's not completely reliable at 4 weeks) because of the price of the PCR test and the rate of false positives. I subsequently visited an emergency room a couple days ago where I was tested for mono, lyme disease, meningitis, etc. Everything was negative. The three Doctors there recommended a PCR test. I'm conflicted. My question: 1. Any idea of how often antibodies show up 3 and 1/2 weeks after infection? 2. What is the rate of false positives for PCR tests? I read somewhere that it is between 3 and 10 percent! Is that true. 3. If so, why the hell are these Doctors telling me to get one?

I would greatly appreciate an answer. Thanks.

Response from Dr. Frascino

Hi,

Visiting an "obviously homophobic" doctor for possible HIV infection is not a wise choice!

Certain types of PCR tests can sometimes be helpful in diagnosing primary HIV infection prior to the development of detectable levels of anti-HIV antibodies in the blood (seroconversion). However, PCR tests should not be used for routine HIV screening, due to the level of false-positives, other technical concerns and cost. HIV-antibody tests (like OraQuick) are not considered to be reliable prior to the three-month mark.

To specifically address your questions:

1. No. Since HIV-antibody tests are not considered to be reliable prior to the three-month mark, there is no good data on the reliability of a 3.5-week test. What I can tell you is that the vast majority of HIV-infected folks will have detectable levels of anti-HIV antibodies in their blood within four to six weeks of primary HIV infection.

2. The rate of false-positives depends on the type of PCR test. For HIV RNA PCR, false-positive tests occur between 2% and 9% and usually at low viral titers of less than 10,000 copies per milliliter.

3. I can't really comment on the advice given by others. What I can do is advise you on the scientific facts that are available and give my personal opinion. Hope that helps.

One final point: Although I'm confident you may now have already learned this lesson well, unprotected sex is not worth the risk!

Good luck.

Dr. Bob



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