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HIV Testing - False Positives
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HIV Testing - False Positives

Hello Dr., and other site readers. Recently, after donating blood, I received a letter stating that my sample had tested postive for HIV with the ELISA testing, but this result had been proven to be false through the Western Blot Test, as well as through Nucleic Acid Amplification Testing. As there are very few threads (that I was able to find) dealing with false positives, I was hoping a doctor could shed a little bit more light on the stats about false positives on the ELISA: How often does it happen? Is there any chance that the ELISA was right while the Western Blot was a false negative? What are the chances the WB and NAT were both wrong? etc etc..

Obviously receiving a false positive on such a life changing test can be a pretty stressful experience, and I'm sure 'anyone' who has been through this would agree, even after hearing "You have nothing to worry about." If anyone else has stories about false positives I'd be more than happy to hear them.

Also, other than just asking for a doctor to share some general facts, I have to say I am looking for some personal reassurance. I know that my case is low risk, but as I said earlier there seem to be very few threads about false positive cases... I am a straight male and I have had vaginal sex with only one girl (whom I know to be fairly promiscuous), on two different occasions. I also performed and received oral sex unprotected from this girl on several (5-6) occasions. Both times a condom  was used, it seemed to be in good shape afterwards, and one of the times was during her menstrual period. I know that viral loads increase during a girl's period, and thus the chances of transmitting HIV increase. I'm pretty sure I know what you're going to say about my specific case, but I need to hear it regardless. As I said earlier, this has been a pretty stressful thing for me. Thanks in advance.
Tags: ELISA
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239123_tn?1267651214
Your follow-up comment below indicates your last test was 7 months after exposure.  You can be 100% certain you don't have HIV, regardless of the initial false positive result.  I'm sure that was disconcerting, but the repeat and confirmatory testing always tell the truth.  I'm not an expert on the frequency of false positive ELISA results with modern testing, but it is rare, less than 1 in several hundred, maybe around 1 in 1000.  In any case, you can be secure in the knowledge you don't have HIV.

I wonder about how the blood bank went about telling you about the initial false positive result.  Of course you would want to know about it, in the event you have future HIV testing--especially a rapid test, when you might be given a result before confirmatory testing.  On the other hand, if/when that happens, the provide has a responsibilty to present the information in the most reassuring manner possible.  (But perhaps they did that.  I'm not criticizing the blood bank, not knowing whether you might have had the same reaction regardless of how the results were presented.)

Good luck--  HHH, MD
7 Comments
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Avatar_n_tn
I'm sorry, I forgot to mention how long after the last possible time of infection I was tested. 7 months, and I know this is well past the window period.
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Avatar_n_tn
Thanks for the reply doc... to answer your wondering.. I received a letter saying  more or less: "Your blood donation tested positive for HIV using antibody screening tests but negative using the Western Blot and Nucleic Acid Amplification Tests. You are considered not infected with HIV."

It's good they didn't tell me the positive before doing the comfirmatory tests, but the way the did it is not comforting at all to someone who prior to this had no knowledge of any of these tests. Take care.
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239123_tn?1267651214
That seems an insensitive and inappropriate mode of communication by the blood bank.  And the terminology "considered not infected" isn't quite as definitive-sounding as something like "These expanded test results show you are not infected with HIV, despite the initial false-positive test result".  I believe they have a responsibility to personally contact such donors, or at a minimum to offer to discuss the results.  It's not as if it comes up all that often; at current false positive rates, for most blood centers it probably comes up only a few times a year.  Feel free to tell 'em I said so; fine with me if you forward this message to them.

HHH, MD
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Avatar_n_tn
Is there a false-negative?
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150689_tn?1333993645
Yes. F-Negs can occur when testing is carried out too early in the window period. Most antibody tests will turn positive after about 21 days (i'm not a doctor and nor is this a definitive answer). But  the vast majority of 4th gen tests are good from about a month and then pretty much bang on after 6 weeks.
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Avatar_n_tn
i had a fasle pos at the 9 and half week mark. i had a reactive elisa a second non reactive elisa a neg p24 and a neg western blot. im waiting for my next tests that i did at the 14 week period. i also tested neg for all the heps at the 14 week period just waiting for the next big one and hope its not the end of my life!!!!!!!
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568933_tn?1216831277
A related discussion, + Rapid then - confirmatory was started.
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Avatar_m_tn
A related discussion, same experience was started.
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