Greetings, Our experience with B27 by flow is very similar. There does not appear to be a truely monospecific antibody on the market. In a study of over 100 patients performed by flow and microcytotoxicity we obtained 4 false positives and zero false negatives using one lambda's antibody. We however are not able to confirm that this is due to cross-reactivity with B44. To the best of my knowledge one lambda does not acknowledge this problem. This is particularly disturbing since their reagent has been FDA approved for stand alone testing. The problem with the reagents is clearly demonstrated in the results of the first two CAP proficiency testing samples of 1996. In these surveys, 33% and 49% of the laboratories incorrectly indentified a specimen (HLA-A1;B37,57(Bw4)) as positive by flow cytometry. This clearly demonstrates the need to confirm all suspected positve flow specimens by an alternate method. Tom Sawyer Medical College of Ohio (419) 381-4212
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