Lifesaving simulations - Organ allocation models in Eurotransplant
Eurotransplant's role is to find suitable recipients when a deceased organ donor becomes available. The allocation is an extensive task as over 13,500 candidates are waiting for a transplant in 203 active programs in 76 centres. To facilitate this process, Eurotransplant has implemented allocation systems, including mechanisms that aim to give patients a fair chance of receiving a transplant. Could these complex systems be further improved to be even more fair? Hans de Ferrante (PhD) recently examined Eurotransplant’s liver and kidney allocation systems with a focus on equality of opportunity. The second objective of his thesis was to develop simulation tools for quantifying the impact of alternative allocation rules on waiting list outcomes in kidney and liver transplantation.
‘Eurotransplant's operations depend on allocation systems with a history of almost sixty years of scientific, legal, and ethical discussions on allocation. The central problem in organ allocation is to determine to which candidates the available organs should be offered.’- Hans de Ferrante
Equality of opportunity
Hans has studied a great deal in his life. He completed two studies - Biomedical Engineering and Econometrics - and did not know what to choose next. ‘Luckily’ he needed a second internship. De Ferrante was triggered by the advertisement for a PhD at Eurotransplant. The combination of working in international medical care and data-analysis seemed just right for him. Now, 5 years later, Hans completed his research and explains the urgency of its topic more in depth in this interview: “Eurotransplant's core value is equality of opportunity. In my thesis, I looked at two areas where this is currently not achieved. My research mainly concerns the allocation of donor organs. Eurotransplant has rules for organ allocation, but in practice the existing rules are not always adequate. For example, is the allocation fair enough? Although the differences are small, women are disadvantaged on the liver waiting list. Immunised patients are also an important topic in kidney transplants. These patients have developed antibodies against donor tissue. Women are more likely to be immunised due to pregnancy. There can also be other causes, such as a blood transfusion. As a result, these specific patients are less likely able to accept donor organs. We found evidence that these factors influence equality of opportunity.”
Concluding through simulation
"We try to compensate these patients within the current rules,” shares Hans, “But that is not always sufficient. My research shows that they have a lower chance of receiving a transplant. The problems have been recognised, but finding a solution is complex. In women, we find that they are often less tall, which means that a large liver, for example, would not fit. You could then adjust the existing 'point allocation system'. But how many points would women need to have the same access to transplantation, and would other patients – such as children – be disadvantaged?
In my PhD, I developed simulators in which we model allocation using data from donors and patients under the existing and alternative rules, with priority given to smaller patients. By using simulators, we can map this out and propose solutions, allowing you to see clearly what happens to the patient group.”
Complex analysis
“One of the challenges is that analyses are more difficult to perform due to the complexity of the data and the process. Careful rules have been drawn up for this over the past 60 years. But we are seeing new rules being added all the time. This has made the system overly complicated. Sometimes we need to simplify!”
'Simulation is not reality. Situations are approached by using a model. That is why Hans is a fan of George Box's quote (1976): 'All models are wrong, but some are useful.' Hans: “You cannot blindly trust models and you must remain critical. We are now at a point where models are useful for structuring discussions and providing insights into what happens when new policies are introduced.'
Liver and kidney projects launched
There is already real-life interest to implement Hans‘ research. “Two projects have been launched for liver transplants. Eurotransplant has used the MELD score to allocate livers. These MELD scores quantify the likelihood of the patient not surviving within 90 days. However, this score does not work for everyone. Some patients have low MELD scores but require access to transplantation for other reasons. For example, patients with liver cancer may urgently require access to transplantation to prevent metastasis and reduce the recurrence risk. These patients currently receive exception points, which increase with waiting time. A drawback of this is that higher MELD scores are required to receive a liver offer, which is especially seen in Belgium, where almost half of the patients receive exception points. With the Belgian Liver Committee, we simulated alternative exception points policies to avoid such a “crowding out” effect. Eurotransplant has now been asked to implement this rule.
Another project Hans was involved in was the introduction of ReMELD-Na for liver allocation. This score was proposed by the LUMC and shown to be a better predictor than MELD in Eurotransplant.
A concern was that the scale of the ReMELD-Na score ranged from 1 to 36, instead of 6 to 40. “If you switch this scale, you must also update the exception point policies; otherwise, patients with exception points could inadvertently receive extra priority. We showed this using the liver simulator.” Partly based on this analysis, liver allocation in Eurotransplant has become based on ReMELD-Na since March 2025.
And there is more. “With the kidney simulator, we are working with the Eurotransplant Kidney Advisory Committee (ETKAC) to take a different approach to kidney allocation. We currently have an allocation system based on a points system from 1996. This system was implemented with the knowledge and simulations available at the time. We would like to make changes to the points system and age matching. You might want the kidneys of a young donor to go to a young patient, simply because they can last longer. Currently, more than half of donors between the ages of 18 and 25 go to people aged 55 and over. We are now discussing this within the Kidney Committee based on the simulation results.”
‘It is important that it is clear what will happen if you change the points system. What are the possible side effects? Do we know what impact this would have on international transfers if we were to implement it? You can now map this out and have a discussion based on figures without any obstacles.’
Lessons learned
"Simulation allows us to show what would happen if certain allocation rules are changed,” explains Hans. “Discussions can then be based on hard numbers. An important message from my research is also that we need more cooperation with the countries, the National Competent Authorities (NCAs) and the committees. The best solution is not always obvious! We have now found a good way of working together for kidney allocation. We look at various topics together and have also presented the simulator to several NCAs. This creates room for evidence-based allocation rules, and shared decision-making with stakeholders in developing allocation rules.”
‘I find the world of transplantation fascinating. The process and the fundamental scarcity are interesting. As is the component of fairness. It's also about policy, and I've noticed that I can influence that through simulations. I think that's cool! It creates consensus and opens new directions. I also enjoy engaging with medical professionals. I work with scientists who are in direct contact with patients for example. They know the basis on which decisions are made in the field, which is something we don't normally get to see at Eurotransplant. The collaboration is very energizing!’
Future visions
Hans aims to improve kidney allocation step by step and giving immunized patients equal opportunities. Hans states that this will help many patients. The kidney is the 'largest' organ within Eurotransplant. There are thousands of people on the waiting list, and the impact of improvements can be huge here. “My hope is that in five years' time we will have modernised the kidney points system and can look back on it with pride and satisfaction!”
De Ferrante would also like to make tissue characteristics matching in kidney allocation fairer. “For some patients, a good tissue characteristic match is easier to achieve than for others. For example, for 15% of patients, such a perfect match is achievable, while that is more challenging for the remaining 85% of patients. Eurotransplant prioritizes a perfect match in kidney allocation, which means that patients for whom this match is less common, may wait longer. The fairness of tissue characteristic matching can thus be improved. There are still many fairness issues that I would like to resolve. Participating more often as a partner in EU consortia would also be a good next step. Eurotransplant is already involved in Leopard and Bravest. Working directly with scientists who work with allocation is a step in the right direction. We could play a more active role in this. There is a lot of knowledge and data here, and we know what happens in certain analyses!”
More info or cooperation?
Would you like to get in touch with Hans de Ferrante for more info or cooperation? Please send an email to request@eurotransplant.org.
The thesis Organ allocation models in Eurotransplant can be consulted via the following link: https://hansdeferrante.github.io/thesis_eurotransplant/.