P163 Antibody identification and detection assays {Lab Screen Mixed (LSM), flow PRA screen, and Single Antigen Beads (SAB)}: Which one to believe?

Abstract

Aim Negative SAB results in the context of positive LSM prevent accurate prediction of virtual crossmatch (XM) in the absence of sensitization history. The issue is particularly problematic in the event of unpredictable positive XM during a deceased donor workup. Unmissed HLA-antibody has to be excluded with certainty by other test. With different assays it may be difficult to choose the best combination. Here we describe the results of correlation between two antibody screening; LAB Screen Mixed using Luminex & FlowPRA Screen on conventional flowcytometry & compare their performance with LAB Screen SAB & XM. Methods 60 samples were tested by the two screening methods according to manufacturer instructions (One Lambda) & tested by SAB for Class I/Class II simultaneously. Sera demonstrated reactivity were crosmatched with surrogate cells bearing the corresponding antigens. Discrepant result was verified by flow specific beads. Results Table 1 summarized the correlation of the results for the three assays. The overall concordance for both screening methods was 72.5% (61.7 for Class I & 83.3 for Class II). In the discrepant results the SAB correlate better with the flow PRA screening. False positive screening was reported only by LSM. Failure of identification of antibody by SAB in presence of positive both screening methods was found in one case (figure1), interestingly the flow PRA of this case was suspicious, DR7 reactivity was confirmed by flow specific bead & weakly positive B-FCXM. In the Four positive cases detected by LSM but not with flow PRA, SAB identify weak antibodies likely to be false positive. Conclusions Flow PRA gives extra evidences about doubtful antibody & provides a rapid risk assessment on the same crossmatch platform.