2-Step Scores with optional nephropathology for the prediction of adverse outcomes for brain-dead donor kidneys in Eurotransplant

Background: The decision to accept or discard the increasingly rare and marginal brain-dead donor kidneys in Eurotransplant (ET) countries has to be made without solid evidence. Thus, we developed and validated flexible clinicopathological scores called 2-Step Scores for the prognosis of delayed graft function (DGF) and 1-year death-censored transplant loss (1y-tl) reflecting the current practice of six ET countries including Croatia and Belgium. Methods: The training set was n = 620 for DGF and n = 711 for 1y-tl, with validation sets n = 158 and n = 162, respectively. In Step 1, stepwise logistic regression models including only clinical predictors were used to estimate the risks. In Step 2, risk estimates were updated for statistically relevant intermediate risk percentiles with nephropathology. Results: Step 1 revealed an increased risk of DGF with increased cold ischaemia time (CIT), donor and recipient body mass index, dialysis vintage, number of HLA-DR mismatches or recipient cytomegalovirus immunoglobulin G positivity. On the training and validation set, c-statistics were 0.672 and 0.704, respectively. At a range between 18% and 36%, accuracy of DGF-prognostication improved with nephropathology including number of glomeruli and Banff cv (updated overall c-statistics of 0.696 and 0.701, respectively). Risk of 1y-tl increased in recipients with CIT, sum of HLA-A, -B, -DR mismatches, and donor age. On training and validation sets, c-statistics were 0.700 and 0.769, respectively. Accuracy of 1y-tl prediction improved (c-statistics = 0.706 and 0.765) with Banff ct. Overall, calibration was good on the training, but moderate on the validation set; discrimination was at least as good as established scores when applied to the validation set. Conclusion: Our flexible 2-Step Scores with optional inclusion of time-consuming and often unavailable nephropathology should yield good results for clinical practice in ET, and may be superior to established scores. Our scores are adaptable to donation after cardiac death and perfusion pump use.