The implementation of the solid phase antibody assays has allowed for the detection and characterization of human leukocyte antigen (HLA) specific antibodies with greater sensitivity and specificity. This information can then be used along with the donor's HLA typing to predict crossmatch results (a virtual crossmatch). Using these data and the level of immunological risk assessed to the antibodies detected, the determination of unacceptable antigens can be made. The calculated panel reactive antibody (CPRA) provides for a means to determine the frequency of these unacceptable antigens in the donor population and thereby predict the probability of a positive crossmatch. In 2009, the Organ Procurement Transplant Network administered by the United Network for Organ Sharing adopted the CPRA as the means to define sensitization and to assign allocation points. Follow-up studies have shown that the number of organ offers refused due to a positive crossmatch has decreased significantly and has saved money through the elimination of unnecessary testing. An additional benefit has been the increased number of sensitized patients being transplanted successfully. Through technical improvements and the refined interpretation of the solid phase antibody assays, continual progress is being made in the definition of the unacceptable antigens and the ability to transplant sensitized patients.