Development and Comparative Evaluation of a Saudi cPRA Calculator for Transplant Sensitisation Assessment

Calculated panel reactive antibody (cPRA) is widely used to estimate the proportion of donors against whom a transplant candidate has unacceptable HLA specificities. Because cPRA is derived from donor HLA frequencies, estimates generated using externally derived donor datasets may not fully reflect local donor compatibility in populations with distinct immunogenetic backgrounds. We developed and comparatively evaluated a Saudi cPRA calculator based on observed HLA phenotypes from 675 local living donors. A total of 250 unacceptable antigen profiles were analysed and entered into the Saudi calculator and three established international systems: Eurotransplant Reference Laboratory (ETRL), Canadian cPRA, and United States Organ Procurement and Transplantation Network/United Network for Organ Sharing (OPTN/UNOS) calculators. System-specific nomenclature harmonisation was performed where required. The cPRA distributions showed a broadly similar shape across the calculators, with mean values of 32.33% for Saudi cPRA, 31.31% for ETRL, 32.30% for Canadian cPRA, and 32.56% for OPTN/UNOS. However, individual profiles showed larger inter-calculator differences in some cases. Spearman correlation coefficients demonstrated strong concordance between Saudi cPRA and ETRL, Canadian, and OPTN/UNOS estimates (ρ = 0.9450, 0.9474, and 0.9560, respectively; all p < 0.001). Bland-Altman analysis showed minimal mean bias across comparisons, although limits of agreement were relatively wide and maximum absolute differences reached 46-48 percentage points in selected profiles. These findings indicate that the Saudi cPRA calculator performs comparably to established international systems at the cohort level, while highlighting meaningful individual-level variation. A locally calibrated Saudi cPRA framework may support more context-specific sensitisation assessment, although further evaluation using larger donor reference datasets and clinically linked transplant outcomes is needed.