Comparison of Flow Panel Reactive Assay (PRA)^TM Specific Test with Complement Dependent Cytotoxicity (CDC) to Define the HLA Antibodies Specificity: A Preliminary Study

To determine the specificity of flow cytometry based assay for HLA antibody screening prior to transplantation, we evaluated 11 positive sera that were tested by both Flow Panel Reactive Assay (PRA) TM class I and class II specific beads after initial FlowPRA TM . HLA specificity was compared with previous data from the complement dependent cytotoxicity (CDC) testing of these samples. We found that five samples (22%) were more HLA class II specific (DR- or DQ-) by FlowPRA TM than CDC. One sample, negative by FlowPRA TM screening, was shown to be HLA class I and class II reactive by FlowPRA TM -specific test. Class I specificity was only defined by CDC in this sample. Two other samples, shown to be HLA class I and class II reactive by FlowPRA TM screening and FlowPRA TM -specific test, were found to be HLA class I reactive only in the first sample and HLA class II reactive only in the second sample by CDC. Our study suggests that FlowPRA TM -specific test has higher specificity and sensitivity than CDC in identification of HLA class II specificity than CDC. Nevertheless, FlowPRA TM -specific test failed to identify precisely the HLA specificity in samples with broad-spectrum specificity, such as those that have HLA specific antibodies directed against large number of shared epitopes. A software protocol for specificity analysis might help overcome this problem. Also, studies involving larger number of samples are required to validate our findings