Perception versus reality ? Virtual crossmatch - How to overcome some of the technical and logistic limitations

The goal of this work was to evaluate concordance between (a) actual flow cytometric crossmatch (FCXM) that is performed by the OPO laboratory servicing our transplant center and (b) virtual XM (vXM) prediction based on antibody identification by solid-phase methods performed in our laboratory. A total of 1586 FCXM, performed between June 2007 and September 2008, between all potential deceased donors in our region and sera from patients awaiting kidney or kidney-pancreas transplant, listed at Northwestern Memorial Hospital were evaluated. A key finding of this analysis was the understanding that a thorough vXM cannot be performed in some donor/recipient pairs due to the lack of certain antibody profile data specific to the donor in question. Obtaining more in depth and stringent information regarding antibody specificities, we demonstrate an excellent sensitivity and specificity of the vXM assays - 86.1% and 96.8%, respectively, with a positive likelihood ratio and negative likelihood ratios of 26.9 and 0.14, respectively. The vXM can serve as an outstanding tool to predict HLA compatibility between donor and recipient, with the caveat that the presence/absence of all antibodies against the potential donor and their strength have been thoroughly investigated.