Making allocation more fair and flexible
Continuous distribution establishes single allocation framework for all organs
The organ donation and transplantation system in the U.S. has never worked better than it does today. Deceased donor transplants have increased for 10 consecutive years, and 26% more organ transplants are performed today than five years ago. But every day, we work to continuously improve and make the system even more effective and efficient to serve all of the patients waiting for a lifesaving transplant.
As part of these efforts, the organ donation and transplant community is working together to introduce a more fair and flexible approach to allocating donated organs to get the right organ to the right patient at the right time. Our policies have always been data-driven, but this new approach applies advanced analytic techniques to create an algorithm that makes every factor in the match run comparable.
Called continuous distribution, this new framework moves organ allocation from placing and considering patients by classifications to considering multiple factors all at once using an overall score. Doing so will dissolve hard boundaries that exist in the current, category-based system and ensure that no single factor determines a patient’s priority on the waiting list.
Learn more about the continuous distribution framework, a timeline for development, and the impact the framework will have on future policy development for all organ types.
How will patients benefit?
- Greater equity among potential recipients
- Better use of the limited supply of organs
- One distribution framework that applies to all organ types
About continuous distribution
In 2018, the Board of Directors approved the Continuous Distribution model for future policy development. It will eliminate edge cases by dissolving hard boundaries and establishing a single allocation framework for all organs.
Organ allocation today
- The current way candidates are prioritized on the waitlist ranks them by placing them into categories, including blood type and antibody sensitization.
- These categories sometimes create hard boundaries that result in inequities for candidates on the edge of a category boundary.
- For example, the current system prioritizes patients with an identical blood type to the donor over patients that have a compatible blood type to the donor, because all things being equal, it’s generally preferable to match identical blood types. However, by placing one category before another, even the most medically urgent patient with a compatible blood type would wait until less medically urgent patients with identical blood types received offers.
A better way
- The new framework moves organ allocation from placing and considering patients by categories such as blood type to leveraging big data analytics and considering multiple factors all at once using an overall score that operates on a sliding scale.
- The composite score for each patient includes all factors—medical urgency, outcomes, candidate biology and efficiency of organ transport.
- In the example above, this means that in the Continuous Distribution framework, an identical blood type patient could receive more points for being an identical blood type match, but a compatible blood type patient could receive more points for having a greater medical need.
- The new framework ensures no single factor determines priority for donated organs.
How it works
Under continuous distribution, candidates listed at hospitals closer to the donor will continue to receive more priority than candidates listed at hospitals farther away. But rather than using specific boundaries to separate “local” from “non-local” candidates—the fixed boundaries used in allocation policy for many years—all candidates will receive priority on a sliding scale formula that balances relative organ transport distance with other important clinical factors.
These other attributes may include medical urgency and the degree of biological match between the donor and the candidate. All of the attributes will be combined into a total score for each candidate, and candidates will receive organ offers based on the total score for each available organ.
Certain factors will have more weight than others, giving them greater influence on the total score. The framework is designed to be easily “tunable.” If data suggests too much emphasis is being placed on one factor and not enough on another, the weights can be increased or decreased for others.
The new system ensures no single factor determines placement.
The new points system and an example match run
Attributes related to the overall score include medical urgency, expected post-transplant outcome, candidate biology, patient access and efficiency of organ placement.
A higher score puts a patient closer to the top of the waitlist and more likely to receive an organ transplant.
In this match run example, each color represents a different attribute and the length of the bar indicates the amount of points given to that attribute. Candidates receive points from multiple attributes and can move up or down depending upon each attribute. Candidate A received the most points in this match run example.
The new system ensures no single factor determines placement.
What happens next?
- All organ systems will transition to Continuous Distribution, but the lung community will be the first.
- A request for feedback paper was available for public comment Aug. 4 – Oct. 1. It outlined the work that has been done so far and invited the community to provide feedback that will inform next steps.
- The committee will review the feedback provided by the community and begin constructing a proposal for modeling and public comment to be issued in 2021.
- Preliminary work has begun to transition kidney and pancreas policy to the Continuous Distribution framework.
- In 2019, the OPTN published a lung concept paper explaining the concepts of continuous distribution
- From 2019 through spring 2020, the attributes were identified that will receive points and contribute to the overall score for each candidate
- During summer 2020 public comment, the community provided feedback through an input survey and a request for feedback paper
- Winter 2020, a sensitivity analysis tool was built to look at how different types of changes could impact the new match run
- Jan. 2021, an analysis was published that looked at data trends of the current system to be able to compare the new system against it
- Feb. 2021, the Scientific Registry of Transplant Recipients (SRTR) modeled four different continuous distribution scenarios to determine potential impact on candidates and recipients
- Summer 2020, the kidney transplantation committee and pancreas transplantation committee began work to identify the attributes that will contribute to an overall score for each candidate.
Our mission is to unite and strengthen the donation and transplant community to save lives.
Learn more about the continuous distribution framework