1.2000
#21
MINIMIZING DISCREPANT LIFEMATCH RAPID SCREEN/LIFEMATCH SPECIFICITY TESTING RESULTS.
Aisha Eltayeb, CHT, Patrick Adams, CHS, Paula Steller, CHS and Charles Orosz, PhD. Columbus OH, USA, Ohio State University, 43210, Clinical Histocompatibility Laboratory.

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Our laboratory uses Lifematch Rapid Screen to initially determine patient alloantibody status. Positive screens are further tested by Lifematch ID to assign antibody specificities. We initially encountered many samples which yielded false positives, particularly in the Class II screening assay. We describe the incidence of false positive results and our strategy to minimize additional testing for these samples. To do this, we analyzed the past 278 sequential sera we had tested in the Lifematch Screen. Samples which were scored as positive, but indicated “adjusted values” < 1.0 when compared to all three control beads included in each assay were considered negative. Using this approach, the incidence of false positive Class I and Class II was 5.4%(n=15), and 33.4% (n=93) respectively. To measure the efficacy of this approach, 96 false positive samples were subsequently tested using One Lambda ClassI/II flowbeads. We observed that 13/15 FP Class I samples were confimed to be negative by the Class I flowbeads and that 71/81 samples were confirmed to be negative by the Class II flowbeads. The risk of “missing” Class I sensitization is 0.7% (2/278) and the risk of “missing” Class II sensitization is 3.6% (10/278). We calculate that the annualized cost savings represented by employing this strategy in our program is approximately $42,000 in product alone for a testing volume of 3,300 specimens per year. We conclude that our algorithm represents a reasonable approach to eliminating specificity testing for this group with minimal risk of permitting alloantibodies to go undetected. Since a pretransplant final crossmatch is mandatory for all patients, we further conclude that employing this strategy poses no risk to the patients.