At any moment, approximately 100,000 individuals in the U.S. are awaiting kidney transplantation. About one-fifth of those receive a new kidney annually, while others unfortunately perish during the wait. In summary, the necessity for kidneys highlights the importance of considering how we utilize this limited resource.
An investigation co-authored by an economist from MIT offers fresh insights into this matter, delivering refined estimates regarding the longevity-enhancing impact of kidney transplants. Accurately assessing this effect can be challenging, yet this research is the first to address several complexities involved, including the choices patients make upon accepting kidney transplants and various pre-existing health conditions.
The study determines that the current system produces an additional 9.29 life-years from transplantation (LYFT) for kidney recipients. (LYFT reflects the discrepancy in median survival between those with and without transplants.) If the organs were distributed randomly among patients, the study concludes, that LYFT average would fall to just 7.54. From this viewpoint, the existing transplantation framework benefits patients overall. However, the study also discovers that the LYFT figure could theoretically rise as high as 14.08, depending on the structure of the matching system.
Regardless, more accurate estimates regarding the advantages of kidney transplants can assist policymakers in understanding the dynamics of the current matching system.
“There’s always this question about how to efficiently allocate the limited number of organs being donated and do so effectively,” notes MIT economist Nikhil Agarwal, co-author of a newly published paper detailing the study’s findings. He stresses that the aim of the paper is to aid in the ongoing enhancement of the matching system, rather than endorse a particular viewpoint.
The paper, “Choices and Outcomes in Assignment Mechanisms: The Allocation of Deceased Donor Kidneys,” is featured in the latest edition of Econometrica. The contributing authors include Agarwal, a professor in MIT’s Department of Economics; Charles Hodgson, an assistant professor of economics at Yale University; and Paulo Somaini, an associate professor of economics at Stanford University’s Graduate School of Business.
Following an individual’s death, there is a window of up to 48 hours where they may be viable organ donors. Prospective kidney recipients are prioritized based on their duration on wait-lists and tissue-type compatibility, and have the option to accept or decline any transplant offer presented to them.
Over the past decade or more, Agarwal has engaged in extensive empirical research regarding matching systems for organ donations, particularly kidney transplants. For this study, the researchers utilized comprehensive data on patients on the kidney wait-list from 2000-2010, provided by the Organ Procurement and Transplantation Network, the national U.S. registry. This enabled the researchers to examine both the matching system and the health impacts of transplants; they followed patient survival rates until February 2020.
This research represents the first quasiexperimental examination of kidney transplants; by meticulously analyzing the decision-making behaviors of kidney recipients, along with various other health factors, the researchers can assess the impact of a transplant, all else equal. Recipients tend to favor kidney offers from younger donors, those without hypertension, individuals who died from head injuries (implying their internal organs were healthy), and those with whom they have an exact tissue-type match.
“The [previous] methodology to estimate the life-year benefits did not consider this selection aspect,” Agarwal comments.
Moreover, a significant empirical characteristic of kidney transplants is that recipients who are overall healthier typically experience the maximum realized life-year benefits from a transplant, indicating that the greatest increase in LYFT is not found among patients in the poorest health.
“One might assume that the sickest individuals, who are most at risk of dying without an organ, would obtain the most benefit [in terms of added life-years],” Agarwal explains. “However, there may be other comorbidities or factors contributing to their health issues, and their bodies may be less capable of sustaining a new organ, thereby reducing the benefits.”
Given this context, the maximum LYFT figure of 14.08 in the study arises from, broadly speaking, a hypothetical scenario wherein a larger number of otherwise healthy individuals receive transplants. Again, the existing system generally prioritizes the duration on a wait-list. Some advocates might propose a system that favors the most ill patients. Keeping all this in mind, the policymaking process for kidney transplants may still necessitate recognizing that the most significant enhancements in patient life-years do not necessarily align with other prioritization criteria.
“Our findings indicate … a dilemma rooted in the conflict between these two objectives,” the authors note in the paper.
To clarify, Agarwal is not promoting one system over another; instead, he aims to conduct data-driven research that allows policymakers to make better-informed decisions during the continuous, long-term endeavor to refine vital transplant networks.
“I don’t believe it’s my comparative advantage to make ethical choices, but we can at least evaluate and quantify some of the trade-offs involved,” Agarwal adds.
The research received partial support from the National Science Foundation and the Alfred P. Sloan Foundation.