Practical application of the virtual crossmatch

Background: HLA antibody sensitization is a risk factor for morbidity and mortality following heart transplantation. We previously reported the results of our in vitro study demonstrating the predictive value of the Virtual Crossmatch (VXM) and have since applied it clinically for sensitized children listed for heart transplant at our center. The VXM utilizes the results of specific antibody screening via flow cytometry to predict acute incompatibility. This review examines the effect of the VXM on wait times and outcomes. Methods: The study population included all patients listed for heart transplantation at Children's Hospital of Wisconsin. Antibody sensitization was defined as PRA > 10% and/or by the identification of HLA specific antibody using AHG-CDC or flow cytometry. Categorical data was analyzed via Fisher's exact test while continuous variables were compared via an unpaired t test. Results: There were a total of 111 listed patients between 7/91 - 9/06. The sensitization rate was 23% (25/111). 19 patients who went on to transplant, deterioration or death were divided into 3 groups depending on listing strategy; Group 1 were listed with a prospective crossmatch requirement, Group 2 with a VXM, and Group 3 with a retrospective cross match. 7/8 patients in group 1 died prior to transplant with median wait time of 119 days. 9/10 patients in group 2 were transplanted with 100% survival and median wait time of 65 days, Group 3 included 1 patient who received a graft after 54 days and died 3 months post transplant with humoral rejection. The VXM was highly concordant with the retrospective crossmatch. Conclusions: Use of a VXM can lead to shorter wait times and better outcomes as a listing strategy for sensitized children requiring cardiac transplantation. The VXM allows transplant physicians to risk stratify patients and consider an anticipated positive crossmatch as one additional factor in the risk-benefit analysis inherent to any donor offer. This experience supports use of the VXM as an alternative to prospective crossmatch requirements. One should recognize that other era dependent improvements such as updated criteria for patient and donor selection along with newer therapies and bridging options may have contributed to superior outcomes seen in the more recent cohort of patients treated with the VXM approach.