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How reliable is a PCR test

Jan 6, 2005

Hello Dr Bob, I would like to congratulate you on your work. I have been reading your forum for the last several weeks and your humor, and compassion are evident, and should be emulated by all health care professionals. After reading the many posts on this site I was not able to find any questions similar to my particular situation. I have been in a monogamous relationship for ten years with a wonderful man. The last several years I have suffered from cluster migraines daily in cycles that range from 2-4 months with 1 month off before the next cycle begins. This has led to some moderate depression which my GP is treating with Zoloft, Zomig nasal for the migraines. With the Holiday season arriving my partner left for his usual 3 month visit with family abroad. Being depressed and feeling alone I had a one night fling with a co-worker. Not something I ever thought would happen, I have always been faithful in the past. This would be the third person I have had sex with and I am 50 years old. Anyway there was some unprotected oral sex involved and insertive anal sex with a condom, however guilt quickly set in and it never allowed me to cum. I don't drink alcohol so it had to be the guilt. So it seems my only risk is from the unprotected oral sex. Lasted about 10 minutes and trust me when I tell you, no deep throating was necessary. It was not until after this incident, that I became aware of the unprotected oral sex risk while discussing my guilt over the whole situation with my best friend. He told me about a new PCR test. My questions are 1. How reliable is this test after 28 days. 2. What is your opinion of my overall risk for HIV 3. If this PCR test comes back negative after the 28 day marker how safe is it to resume the status quo with my partner or should we wait until my ELISA results come back after 90 days. It has been 2 weeks and I have no signs of infection, my only symptoms are loss of sleep which I attribute to guilt and anxiety. My partner and I have both been vaccinated for Hepatitus A & B, as every gay man should be. Thanks for your time Dr Bob and I will be sending a donation because I feel this site has kept me from losing my mind with worry.

Response from Dr. Frascino


In general, PCR testing is not recommended for routine HIV screening, due to false-positive results, cost and other factors. The standard serological test consists of a screening EIA followed by a confirmatory Western Blot (WB). EIA screening requires a "repeatedly reactive" test, which is the criterion for WB testing.

That said, PCR testing can be either DNA or RNA. False-positives with HIV RNA PCRs can range from 2% to 9%, and are most frequently seen at low viral titers. As for your overall risk, unprotected oral sex carries a very low risk for HIV transmission. Protected insertive anal sex would indeed be "protected," if the latex condom was used properly and did not fail.

Thank you for your donation!

Good luck.

Dr. Bob

I'm so worried!!! Please help me doc!
Positve skin test for TB?

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