Impact of DP in CPRA Calculation

Abstract

The algorithm for determining CPRA values that incorporate two or more of the HLA-A, -B, -C, -DRB1, -DRB3-5, -DQA, and -DQB loci requires information about the frequencies of alleles at the various loci as well as of the haplotypes comprised of the loci to which a patient has antibodies. Increasing awareness of the relevance of antibodies to HLA-DP has made it desirable to include DP in the CPRA calculation. DPB alleles sort independently from HLA alleles telomeric to DPA and therefore, do not require the frequencies of DP haplotypes for incorporation into CPRA. Calculations of CPRA that include DP incompatibilities (CPRA-DP) were performed according to the following algorithm: CPRA-DP = 1 − p2 (1-CPRA) where p is the sum of the frequencies of compatible DP alleles and CPRA is the currently used CPRA calculation. DP alleles frequencies were determined from 1082 deceased donors typed in our laboratory. CPRA-DP was determined for patients grouped by traditional CPRA values for varying degrees of DP incompatibility. As expected, the impact of DP incompatibility was greatest for patients with the lowest CPRA values and decreased as CPRA values increased. Depending on the specificity of the DP antibodies, including DP in the CPRA was shown to make a substantial difference in all but the highest CPRA categories. Given the addition of a sliding point scale for CPRA and prioritization for the highest CPRA candidates in the new kidney allocation system (KAS), the addition of DP to the CPRA calculation would benefit all candidates with DP antibodies. Download full-size image