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Pos EIA, Neg WB (POSITIVE ELISA, NEGATIVE WESTERN BLOT)
Sep 14, 2008

I am a 30 year male who had unprotected vaginal intercourse with a female I did not know almost 3 months ago. I got tested at 9 weeks after exposure and the ELISA came back positive and the WB came back negative with no bands. The test was repeated at around 11 weeks with the same result. However this time, a PCR was also done which came back complately negative. I'm planning to do another test once the 12 week period is over. Should I be very worried that the ELISA keeps coming back positive? Does the PCR result mean anything or is it too early to tell?

Thanks,

Caustiously opptimistic

Response from Dr. Frascino

Hi,

A positive EIA (or ELISA) and negative confirmatory Western Blot is read as a negative HIV-screening test. This situation is not uncommon and I've addressed it many times before in this forum. I'll reprint some examples below from the archives.

Regarding HIV testing in general, the recommended screening test is an HIV-antibody test (ELISA, EIA, rapid test) at the three-month mark. HIV-antibody tests taken prior to the three-month mark are not considered to be definitive or conclusive. PCR testing is not recommended for routine HIV screening, due to the rate of false-positives, other technical considerations and cost. That said, that you've had a negative screening test (positive ELISA plus negative WB equals a negative test!) and an undetectable PCR test out to 11 weeks is reason to be much more than "caustiously optimistic." I say it's essentially WOO-HOOable.

Dr. Bob

positive elisa Feb 15, 2008

I was date raped almost a year ago this month. I took HIV tests at 60 and 90 days. At 7 1/2 months I took another test and that one was positive elisa and negative western blot. I am now pregnant and in routine prenatal labs I had another positive elisa. The western blot is not yet in, my question is, what are the chances that I have it? The only possible risk was unprotected oral sex and I believe he used a condom for vaginal and anal sex. I am scared for my baby. Please help.

Response from Dr. Frascino

Hi,

A positive ELISA and negative Western Blot is considered a negative HIV test! ELISA tests can be falsely reactive due to many factors, including nonspecific cross-reacting proteins resulting from pregnancy. Assuming your pending Western Blot is once again negative, I see no cause for concern. You can read more about false-positive ELISA tests in the archives.

Good luck.

Dr. Bob

False Positive Jul 17, 2007

Dr. Frascino,

Hi. My partner and I have been together for two years. He has been HIV positive for 13 years and his viral load is undetectable. He remains exceptionally healthy. We do not practice safe oral sex. For precautionary measures, I have 3-4 HIV tests per year. In May 2007, my Elisa test came back positive and the Western Blot negative. My PCP referred me to an infectious disease specialist because of the situation with my partner being positive and me being negative. In July 2007 the tests with the specialist returned the same results. My question is why? Over the past two years, four out of six tests returned a negative Elisa, while my last two returned a positive Elisa with an negative Western Blot. The specialist stated the virus may be in the early development stages, but again, unlikely because my viral load is at 400 or undetectable. What are the reasons for the positive Elisa with a negative Western Blot?

Thank you for your time.

Response from Dr. Frascino

Hello,

A reactive ELISA and negative Western Blot (WB) is considered a negative HIV-screening test. The ELISA test is set to pick up as many true positives as possible (very sensitive test). In doing so it also picks up some "false positives." That's why a reactive ELISA must always be followed-up with a confirmatory more specific test, such as a Western Blot or immunofluorescence assay (IFA), to confirm the reactive ELISA before the test (combined ELISA and WB) can be termed "positive." There are many reasons why ELISAs can show "false positive" results, including cross-reacting nonspecific antibodies that trigger a positive result, but that have nothing to do with HIV.

If your results are in dispute or should your Western Blot become indeterminate, which can also happen with nonspecific cross-reacting antibodies, I would recommend you get a DNA PCR (rather than RNA viral load).

Considering your two reactive ELISAs had negative WBs and were run two months apart, I strongly doubt you are seroconverting.

Dr. Bob

Positive Elisa Negative WB Jul 31, 2008

I recently had an HIV test (July 22) after having several rounds of vaccinations for school 1 month earlier. For the first time my ELISA came back positive, my WB came back negative (no bands). I have had NO unprotected sex in the last 6 months but had sex with 1 female protected and no fluids were exchanged (no kissing, etc). When the lab technician got my test results she walked me outside and told me i can be sure i have HIV and though she'd never seen this result in her 11 years the virus is simply lying dormant. Have you seen this in your experience?

-Worried

Response from Dr. Frascino

Hello,

The lab technician told you that you "can be sure (you) have HIV"????? WHAT???? Apparently that lab technician is not the brightest bulb in the tanning bed (so to speak). A reactive (positive) ELISA with a negative Western Blot (WB) is considered to be a negative HIV test, because the WB is the more specific test. Also, HIV doesn't lie dormant! Someone needs to send that technician to an HIV refresher course.

Positive ELISAs with negative WBs are quite common. That the technician had never seen this result in her 11 years is rather surprising. Are you sure she was a real technician? She seems as clueless as Dubya faced with a word that has more than three syllables.

Take a look through the archives. We have a whole chapter devoted to HIV testing. There you will find many cases similar to yours.

Dr. Bob



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