Study on organ donationsOpt-out system does not automatically mean more available organs

Photo: Adobe Stock/Alexander Raths

In Germany, organ donors have to explicitly provide consent, for example, by presenting a donor ID.

In Hamburg, the number of donated organs in 2024 rose slightly from 154 to 160. Nationwide, however, 0.8 percent fewer organs were donated than in 2023. Overall, there were strong fluctuations in the willingness to donate organs and policymakers have ongoing discussion about legal alternatives for organ donation practices. One suggestion is the so-called “opt-out” system. Everyone in Germany should, as a rule, be deemed a potential donor, unless they actively object or “opt out.” This should lead to more organs for transplants. 

A current study involving researchers from the University of Hamburg Business School has now shown that this approach would not necessarily increase the number of organ donations. A comparison with data from 24 countries revealed that the countries that have switched from the consent to the opt-out system have actually seen a decrease in living organ donation, on average by about 29 percent. At the same time, with the opt-out approach, the so-called postmortem donations rose by an average of only 7 percent, because there are potentially more organs available after a death but these cannot always be used as donations. Overall, this meant no increase in organ availability.

Under the leadership of Prof. Dr. Michel Clement, researchers from the University of Hamburg and the Vienna University of Economics and Business also conducted experimental studies with over 5,000 subjects to look at the consequences of a shift from the “opt-in” to the “opt-out” approach. In Austria, unlike in Germany, the opt-out principle is already in place.

“We conducted comparative analyses of organ donation numbers and, in parallel, conducted surveys on willingness to donate in both countries. Our focus was scenarios with different rules and their effects,” explained Clement. The professor of marketing and media at the University of Hamburg Business School continued: “The results confirm the repression effect yielded by the data analysis: people who live in countries with an opt-out system think the organ donations are more available and thus less willing to become a living organ donor themselves.” This, Clement said, is not applicable for donors who give to their closest family members, but is true for so-called “altruistic donors” who give to distant relatives, acquaintances, or strangers.

In Germany, living organ donors in 2024 constituted 18.6 percent of all transplants, according to the Deutsche Stiftung Organtransplantation. Kidneys and parts of the liver, especially, involve living organ donations and transplants. In 2024 in Germany, almost 6,400 people waited for a kidney donor. The study’s authors recommend taking possible “repression” effects into consideration when discussing the introduction of an opt-out system. “An opt-out regulation should be part of a larger overall strategy that, above all, clarifies, discusses, and involves all of society in a critical approach to the topic,” said Clement.

Original publication:

Pascal Güntürkün, Sinika Studte, Daniel Winkler, Michel Clement, Jonathan H W Tan, Eva-Maria Merz, Elisabeth Huis in ‘t Veld, Eamonn Ferguson. 2025 “Crowding-out effects of opt-out defaults: Evidence from organ donation policies,“ PNAS Nexus, Volume 4, Issue 10, October 2025, pgaf311, https://doi.org/10.1093/pnasnexus/pgaf311