Vivian's experience is basically the same as ours with the B-D kits. We are a regional testing center for B27 and use the kit to screen the 200-300 samples per month. From initial pilot data we developed a screening scheme for "gray-area" flow results representing B27 fluorescence intensities near the B-D "cut-off" channel number (+/- 6 channel numbers). Those within this range represent about 10% of our samples, and we immediately send these to cytotoxicity or DNA typing for confirmation. Of those only 50% turn out to be false positive or negative (cytotoxicity as "gold" standard), with about equal distribution of negatives and positives. Of false positive, 75% are B7+ (cytotoxicity or DNA). Since this represents only 2% of our work load, it does not make sense to further test for B7 in flow. The false negatives are not easily explained although some relate to overall loss of class I expression, tested in flow using the W6/32 mAb. In all, the B27 results are >95% accurate, and fairly inexpensive (even by B-D standards of inordinate cost!!!), compared to cytotoxicity alone or testing in conjunction with SSP DNA. As I see it the cytotoxicity tests have never been examined to a reliability of 95% so some of the "discrepancies" could be related to variability in the cytotoxicity accuracy in a given laboratory. So for large volume, the B-D reagents are economical and a very reliable screen. In the tough cutback times for Health Care in southern Ontario, that has a "real" meaning. Of course, if you expect to have a large volume such as ours, you should try to "extract" a little compensation in reagent cost from B-D. Good luck, Denis Snider >
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