Evaluation of the flow cytometric crossmatch. Preliminary results of a multicenter study

The flow cytometric crossmatch is a technique that is increasingly being used by clinical transplant laboratories. In this multicenter study by the British Society for Histocompatibility and Immunogenetics Flow Cytometry Group, a series of crossmatches were carried out to determine whether different centers obtained same results when performing the same crossmatch. There was greater than 80% agreement among participating laboratories on the results of 35/54 tests. There was no clear agreement in the remaining 20 cases. Quantitative analysis, estimating the number of cell-bound fluorescein molecules, demonstrated that differences in the criteria used by each center to define a positive crossmatch were responsible for some discordant results. When applied, definition of positivity based on the molecules of fluorescein increased concordance from 57.5% to 81.4%.l. These results suggest that a criterion for the interpretation of results based on quantitative analysis of bound antibody may be more reliable than methods in current routine use.