The ETKidney simulator: a discrete event simulator to assess the impact of alternative kidney allocation rules in Eurotransplant

TL;DR

The ETKidney simulator addresses the need for quantitative policy assessment of ETKAS and ESP by implementing Eurotransplant-specific allocation rules within a Discrete Event Simulation framework. It reproduces the March 2021 ETKAS/ESP rules, incorporates a balance system, and uses synthetic data with counterfactual imputations to enable input–output validation against real-world outcomes from 2021–2024. Through three case studies, the paper demonstrates how reallocating weight among HLA loci, introducing a vPRA sliding scale, and applying candidate-donor age matching can alter transplant rates, access, and long-term outcomes, while highlighting trade-offs and potential unintended consequences. The ETKidney tool holds promise for informing policy decisions with transparent, case-based analyses, and is publicly available to support collaboration with policymakers and researchers, albeit with acknowledged limitations and a path for ongoing refinement.

Abstract

Over 10,000 candidates wait for a kidney transplantation in Eurotransplant, and are prioritized for transplantation based on the allocation rules of the Eurotransplant Kidney Allocation System (ETKAS) and Eurotransplant Senior Program (ESP). These allocation rules have not changed much since ETKAS and ESP's introductions in 1996 and 1999, respectively, despite identification of several areas of improvement by the Eurotransplant Kidney Advisory Committee (ETKAC). A barrier to modernizing ETKAS and ESP kidney allocation rules is that Eurotransplant lacks tools to quantitatively assess the impact of policy changes. We present the ETKidney simulator, which was developed for this purpose. This tool simulates kidney allocation according to the actual ETKAS and ESP allocation rules, and implements Eurotransplant-specific allocation mechanisms such as the system which is used to balance the international exchange of kidneys. The ETKidney simulator was developed in close collaboration with medical doctors from Eurotransplant, and was presented to ETKAC and other major stakeholders. To enhance trust in the ETKidney simulator, the simulator is made publicly available with synthetic data, and is validated by comparing simulated to actual ETKAS and ESP outcomes between 2021 and 2024. We also illustrate how the simulator can contribute to kidney policy evaluation with three clinically motivated case studies. We anticipate that the ETKidney simulator will be pivotal in modernizing ETKAS and ESP allocation rules by enabling informed decision-making on kidney allocation rules together with national competent authorities.

Figures (8)

• Figure 1: Flow chart on how Eurotransplant offers kidneys for kidney-only transplantation. The percentages shown represent the proportion of kidney-only transplantations performed through each mechanism between 2014 and 2023 etStatsLibrary2072P. Kidneys declined in ESP by all candidates were re-allocated via ETKAS until March 2021. Since March 2021, an extended allocation is triggered to place such kidneys.
• Figure 2: Event handling flowchart for the ETKidney simulator. Inputs and parameters are represented using parallelograms. In case a kidney was declined by all candidates, simulation settings determine whether a discard is recorded or whether a candidate is forced to accept the kidney for transplantation. FES: Future Event Set.
• Figure 3: Summary of how Eurotransplant's kidney offering process is approximated by the ETKidney simulator.
• Figure 4: Relations between the relative transplantation rate and vPRA in ETKAS, estimated on ETKidney simulator outcomes. These relations were estimated with a Cox proportional hazards model, adjusting for the vPRA using spline terms.
• Figure 5: Estimated relations between graft loss and death with a functioning graft. Note that the hazard ratio for death with functioning graft is shown on the logarithmic scale.