Small reductions in cPRA are associated with increased kidney transplantation in 100% cPRA patients. However, the high level of antibody in these patients is such that desensitization may reduce antibody but not cPRA, thus the cPRA change on undiluted serum with desensitization is an insensitive measure of effectiveness. We evaluated cPRA reduction, calculated per antibody titer, as a desensitization trial endpoint. To accomplish this, 2 serum samples from 20 kidney transplant candidates with cPRA ≥99.9% (100%) were obtained and serially diluted in triplicate to determine the titer of individual HLA antibody specificities. CPRA was computed per dilution to identify the titer at which cPRA drops below 98%. Inter and intra assay variability and changes overtime were determined. The dilution needed to reach a cPRA 2 titers can be deemed clinically meaningful. The median (IQR) titer difference was 0 (0-1) from baseline to follow-up within 12 months. The cPRA per titer also risk stratified candidates for trial inclusion. In conclusion, determining the cPRA per titer is a reliable approach to simplify complex antibody data and an ideal endpoint for desensitization trials.
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