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Old 03-01-2005, 05:47 PM
Loopydude Loopydude is offline
Join Date: Dec 2003
Posts: 8,299
Even in the absense of detectable antigen, it's not a stretch to suspect you've been exposed if there's detectable antibody against HepB antigens in your serum.

It's also worth considering that antibodies are not perfectly specific for a particular protein. Sequence and structural similarties with other proteins may allow a particular monoclonal antibody to cross-react with any number of other proteins that contain a motif sufficiently similar to the antigen that generated the immune response you clearly manifest. Whether it's due to true Hep B exposure, exposure to another similar virus, or something else entirely that just happens by pure chance to be similar, is difficult to determine, and well outside of the means of the blood banks attempting to regulate the safety of their inventories to establish. In all but the most benign permutations of the latter case, you may pose a risk to a recipient; there's just no practical way to know for sure. They have peformed an immunoassay that gave a positive result, and based on that result have acted according to their guidelines. Their guidelines do leave certain questions unanswered, but it's no feasible for them to answer those questions, so they must remain moot.

Just because of where I've been in the world, and for how long, I cannot now donate blood (CJD risk-assessment preculdes it). I'm in the same boat, essentially, and sympathize with your disappointment. Unfortunately, there's nothing for it but to seek other outlets for performing civic duties.