Important note: Information in this article was accurate in 2004. The state of the art may have changed since the publication date. I have been a blood donor for thirty years without any problems, but when I donated in May 2004 I received a letter from the Blood Center saying I tested positive for HIV antibodies but that the more specific confirmatory test read negative indicating I did not have the HIV virus. Still they put me on a six month deferral list for donating. My previous donation was in February 2004 and had no HIV antibody indication. I'm curious why I would, after all these years of donating ,suddenly have a false positive reading? Also, if I was "clean" in February when I donated and say for some reason the follow-on blood test I took two days ago were to come back HIV positive, when would be the earliest I could have contracted it. I've been with the same woman, and have only had sex with her, since October 2003. Before that would have been with a previous girlfriend in mid-August 2003. It's pretty obvious why I'm asking, if I am HIV positive I'd like to narrow it down to whom I got it from. Thanks!
Mark H. Katz, M.D.
Regional HIV/AIDS Physician Coordinator
Kaiser Permanente of Southern California
Blood screened for HIV goes through a process whereby it is first tested with a highly sensitive assay known as the ELISA. The ELISA is meant to pick up all HIV--and hosts of other things that are not HIV but might have some chemical reactivity which is similar. Thus, the goal here is to not miss a single case, but at the cost of having many so-called false positives. This is why any positive ELISA must be confirmed with the very specific so-called Western blot.
In normal HIV testing (not referring to blood donations here), a positive ELISA and negative Western blot is reported as a negative. In other words, such a combination means one does not have HIV. The only real potential exception, and hence your letter, is that the ELISA may turn positive a bit earlier than the Western blot, so they are wanting you to "make sure" you are not in the early weeks of seroconverting. Since your last encounter was months earlier, it would have already shown up as Western blot positive if you had acquired HIV.
Thus, you did not! The list of things which can give false positives is vast. They include other viral infections, certain disease states (e.g. lupus, other autoimmune conditions), pregnancy, etc. If you were to do another HIV ELISA now, it might well be negative.
Good luck!
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