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Medical Forum / General / General / September 2007Hepatitis B -- retest
Following up on my postings from last month -- when I discussed how I had tested positive (reactive) on the hepatitis B core antibody test, but negative on several other hepatitis B tests: My local blood bank offered to retest me, using a new and improved hepatitis B screening test (the PRISM test) which they had recently started using. The results just came in, and this time I tested "non-reactive" for the hepatitis B core antibody (combined IgG + IgM). The people at the blood bank believe this means my earlier, reactive anti-HBc results (from the blood bank in 2001, and from my doctor in 2003) most likely represented false positives -- i.e., that I had in fact never been exposed to hepatitis B after all, and that my blood most likely was (and is) safe for transfusion to others. Now, it might be worth noting that my score on the new test, though definitely in the non-reactive domain, was slightly iffy. On a scale where the dividing line is 24,000, and figures higher than 24,000 are considered non-reactive, my measurement was 30,000. According to the blood bank expert who discussed the test with me, most of the old "false positives" retested using the new test have been measured at around 40,000. I was told it wasn't clear just what my "weakly non- reactive" score means -- e.g., just what might be causing my blood not to score as "high" on the test as others who were non-reactive -- or, alternatively, if in fact I really have been exposed to HBV, how long ago I would need to have been exposed for my immunity to be as distant as it would have to be to explain all the other negative test results. In any case, I've been told that I'm welcome to donate blood again, and that it's unlikely (not totally impossible, but unlikely) that I'll test "reactive" in the future on the new hepatitis B screening test. Comments from anyone on the new PRISM screening test, the "false positive" interpretation of the old results, my "slightly non- reactive" score on the new test, whether my blood really is safe, or anything else? Rich Wales richw@richw.org http://www.richw.org *DISCLAIMER: I am not a doctor. My comments are for discussion pur- poses only and are not intended to be relied upon as medical advice. >Following up on my postings from last month -- when I discussed how >I had tested positive (reactive) on the hepatitis B core antibody [quoted text clipped - 10 lines] >fact never been exposed to hepatitis B after all, and that my blood >most likely was (and is) safe for transfusion to others. One problem with all such tests is that antibodies produced in response to an antigen can be very idiosyncratic. Depending on genetics and combinatorics, there can be great variation in the sequence of the antibody individuals will produce to the same antigen, so there's always going to be false positives to these tests for people who've raised an antibody to something completely different that cross- reacts with the antigen used in the test. Some years ago the flu vaccine from a particular manufacturer caused a small fraction of recipients to have false positives to an HIV test. Some antibody you've raised to something like a particular cold virus or almost anything else just happens to cross-react with the antigen used in the older form of HepB test and not with the newer one. >Now, it might be worth noting that my score on the new test, though >definitely in the non-reactive domain, was slightly iffy. On a scale [quoted text clipped - 14 lines] >I'll test "reactive" in the future on the new hepatitis B screening >test. The Canadian Blood Service is *really* paranoid these days about risks in the blood supply. The cut-off of 24,000 is probably very conservative. Again, some antibody you've produced just happens to cross react to the antigen used in this test too, but much less strongly than to the previous one. >Comments from anyone on the new PRISM screening test, the "false >positive" interpretation of the old results, my "slightly non- >reactive" score on the new test, whether my blood really is safe, >or anything else? The CBS, super-cautious about these issues, thinks your blood is okay. If I were you, I'd believe them. Disclaimer: I'm neither a doctor nor an immunologist. I welcome corrections from the more knowledgable. > The Canadian Blood Service . . . super-cautious > about these issues, thinks your blood is okay. Thanks. Please note, BTW, that I currently live in the US, so the relevant agency in my case is the FDA. Rich Wales richw@richw.org http://www.richw.org *DISCLAIMER: I am not a doctor. My comments are for discussion pur- poses only and are not intended to be relied upon as medical advice. > > The Canadian Blood Service . . . super-cautious > > about these issues, thinks your blood is okay. > >Thanks. Please note, BTW, that I currently live in the US, so the >relevant agency in my case is the FDA. Ah. I thought you still lived in K-W, Ont. > Following up on my postings from last month -- when I discussed how > I had tested positive (reactive) on the hepatitis B core antibody [quoted text clipped - 38 lines] > *DISCLAIMER: I am not a doctor. My comments are for discussion pur- > poses only and are not intended to be relied upon as medical advice. Thanks for the follow-up. With any new tests out there there is a learning curve with it. There are usually gray zone results or borderline results which ever you prefer. I presume it was not in such gray-zone area. The obvious other question is the precision of the instrument. There are a variety of new instruments by Abbott including Prism. I would not be too enamoured with some of the hype given by sales reps as the warts will show sooner or later with regards to sensitivity or specificity. Some hepatitis testing with recent platform instruments have been pulled from the market and only time will tell. As to whether your blood is safe or not the BB has the final call on that. Your NAT HBV is negative. Some have proposed getting rid of anticore testing. The studies and discussion about that along with the some mention of Abbott Prism testing can be seen here, scroll down aways. There is a very remote chance that one can transmit the virus with all the testing you have had. http://www.fda.gov/cber/minutes/nuclacd1205p1.htm |
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