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TITLE: ELIMINATING UNNECESSARY CROSSMATCHES FOR HIGH PRA RECIPIENTS BY IDENTIFYING UNACCEPTABLE ANTIGENS USING HIGH DEFINITION FLOW CYTOMETRIC BEADS

Walter F. Herczyk, ¹, Barbara O. Burgess ¹, Janet E. Tuttle-Newhall ² and Nancy L. Reinsmoen ¹.

¹Pathology, Duke Medical Center and ²Transplant Surgery, Duke Medical Center, Durham, NC, United States.

Highly sensitized (>80% PRA) patients on the solid organ wait lists receive additional points for possible organ allocation; however, the crossmatches are usually positive since unacceptable antigens are difficult to identify in these cases. The high definition single antigen flow beads in combination with the specificity analysis flow beads (One Lambda, Inc.) allow for the accurate identification of antibody specificities for these highly sensitized patients. We have used these flow bead reagents to identify unacceptable antigens for our sensitized kidney, heart, and lung patients on the wait list. To determine if the PRA analyses accurately predicted the crossmatch results, we analyzed the results for 10 consecutive highly sensitized patients called in for final crossmatches. Of the 10 patients, 5 had PRAs >80% and 5 had PRAs ranging from 46 - 67% (anti-class I +/or II). A total of 14 donor specimens was tested by CDC-AHG and/or flow cytometry crossmatches for these patients over a 3 month period. The high definition unacceptable antigen analysis accurately predicted 9 positive crossmatches and 5 negative crossmatches (100% concordance). Based on these results, we have used the unacceptable antigens defined by high definition beads to select patients for final crossmatches. During the past 6 months, the average positive crossmatch rate was 16% (19/97 donors tested) compared with 26% (27/103) for the same 6-month period during the previous year. Locally, 30% of recipients transplanted had PRAs >20% compared with the national average of 11.26% (p=0.0001). Thus, identifying the unacceptable antigens by flow beads has reduced the positive crossmatch rate by 39%, while allowing for a significantly higher percentage of sensitized patients to be transplanted locally than the national average. An accurate assessment of unacceptable antigens for these patients will decrease the cost for crossmatching, facilitate rapid organ allocation, and decrease the time and cost associated with patients traveling to the transplant center unnecessarily.