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Continuous distribution

Creating a more fair and patient-focused system for organ allocation

Video: How is continuous distribution different from the current system?

Video: How does the points-based allocation system work?

Each organ type's final continuous distribution policy will be adopted by the OPTN Board of Directors, and will comply with NOTA and the OPTN Final Rule.

How will patients benefit?

  • It’s a more fair and flexible system, because multiple factors will be considered at the same time
  • Equity is predicted to increase among potential recipients
  • Patients can provide their feedback earlier in the policy development process
  • It’s a single distribution framework that can be adapted to all organ types

Creating a new system: Goals and driving principles

The Organ Procurement and Transplantation Network is developing a more equitable system of allocating deceased donor organs. The new approach is called continuous distribution.

The goals of the new continuous distribution framework are consistent with allocation requirements in the National Organ Transplant Act (NOTA) and the OPTN Final Rule.

Continuous distribution goals

  • Prioritize sickest candidates first to reduce waitlist deaths
  • Improve long-term survival after transplant
  • Increase transplant opportunities for patients who are medically harder to match
  • Increase transplant opportunities for candidates with distinct characteristics like candidates under the age of 18 or prior living donors
  • Promote the efficient management of organ placement

This new framework is being designed to allow multiple factors that contribute to a successful transplant to be considered simultaneously as part of the organ offer process.

The current system

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The current system creates hard boundaries that can stop a transplant candidate from being prioritized further on the match run.

CURRENT SYSTEM: Why does it need to evolve?

Right now, a classification-based system of organ allocation is in place. The current system gives points to candidates at various steps of a sequence in the organ offer process. Candidates are transplant patients who are waiting for an organ to be offered to them.

That can mean that when certain candidate characteristics, called attributes, are reviewed in sequence, sometimes patients are placed on one side of a hard boundary that stops them from being prioritized further on the match run. The match run is the list that is generated when an organ donor’s information is entered into the national waiting list computer system, to identify potential recipients.

Some examples of a candidate’s attributes or factors include:

  • Medical urgency
  • Distance from the donor hospital
  • Biology
  • Expected outcomes

CURRENT SYSTEM: How does it work?

The current system that matches organs with patients gives points to candidates at various steps of a sequence in the organ offer process.

EXAMPLE

In this broad example, there are four candidates who are being prioritized for an organ offer: Candidates A, B, C and D.

These patients vary in terms of their:

  • Medical urgency
  • Distance from the donor hospital
  • Candidate biology (compatibility)
  • Predicted one-year post-transplant survival
Graphic of a map with four candidates labeled in different locations on a map of the eastern United States surrounding a donor hospital. Below the map is a table with different values for four different factors for each candidate that is identified by letters A, B, C, and D. The medical urgency factor gives Candidate A a medium value, Candidate B a high value, Candidate C a low value and Candidate D a medium value. Distance from the donor hospital gives Candidate A a 249 NM value, Candidate B a 251 NM, Candidate C 230 NM, and Candidate D a 300 NM. The candidate biology (compatibility) factor gives Candidate A a medium value, Candidate B a low value, Candidate C a medium value, and Candidate D a high value. The 1 year survival after transplant factor gives Candidate A a high value, Candidate B a medium value, Candidate C a high value, and Candidate D a low value.

In the current classification system, any single factor could potentially determine the order in which these candidates are prioritized in a match run.

For example, if the order of prioritization were to be based first on distance, then Candidate C would receive an offer first, followed by A, B and D.

But if priority is given to the patient’s medical urgency, then Candidate B would receive the first offer, followed by A, D and C.

As this example shows, the current classification-based system sometimes places patients on one side of a hard boundary that stops them from being prioritized further, because patient factors aren’t considered together.

The new system: Continuous distribution

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The new continuous distribution framework will:

  • Dissolve the hard boundaries that exist in the current system
  • Change how patients are prioritized by considering all patient factors together

NEW SYSTEM: How does it change organ allocation?

The new continuous distribution framework will dissolve the hard boundaries that exist in the current classification-based system. Importantly, continuous distribution is flexible enough to apply to all organ types.

Continuous distribution will change organ allocation by:

  • Considering all candidate attributes at the same time, rather than placing patients into rank-ordered classifications
  • Ranking candidates with an overall score that is calculated using multiple patient attributes, as well as efficiency of organ placement

Video: Organ allocation: questions and goals

Working organ type by organ type, through research and analysis, the donation and transplantation community is working together to design this framework to determine patient priority in the match run.

NEW SYSTEM: How are patients prioritized?

Continuous distribution will change how patients are prioritized. Continuous distribution will consider all patient factors together to determine the order of an organ offer, and no single factor will decide an organ match. The goal is to increase fairness by removing the hard boundaries that are part of the classification-based system.

Every organ type will have its own formula to calculate how candidates on the waiting list are prioritized. Depending on the formula that is chosen for a specific organ type, Candidate B in the example above may be the first to receive an offer based on a combination of high medical urgency, medium survival probability and moderate distance from the donor location.

All the factors will be considered together, but every factor will also be weighted. Depending on the weighting of the various factors, the remaining order in the example above may be A, C and D. Candidate C, with the shortest distance from the donor hospital, might appear ahead of Candidate D, who has medium medical urgency but is the farthest from the donor location.

NEW SYSTEM: Points system and composite allocation scoring

Patients in the continuous distribution system will receive a composite allocation score. Attributes related to a patient’s 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 a match run and more likely to receive an organ transplant.

Specific attributes labeled in boxes in a line next to each other separated by plus signs. Medical urgency plus post-transplant survival plus candidate biology plus patient access plus patient efficiency equal a patient’s composite allocation score. Mobile image. Specific attributes labeled in boxes in a line next to each other separated by plus signs. Medical urgency plus post-transplant survival plus candidate biology plus patient access plus patient efficiency equal a patient’s composite allocation score. Desktop image.

NEW SYSTEM: Attributes and the goals

Every organ type will have a specific set of attributes that will be considered. These attributes will tie to a number of goals such as prioritization of the sickest candidates and increasing transplant opportunities for patients who are medically harder to match.

Visit each organ type’s continuous distribution page to learn about their specific attributes and the goals they support.

Lung Kidney and pancreas

Understanding attributes and points in a match run

Bar chart that represents a potential match run with candidates A through E. Each bar represents a single potential candidate and contains stacked sections of different colors that indicate number of points received for each attribute. In this example match run, candidate A received the greatest amount of points and the highest overall score.

In this general match run example (not specific to any organ type):

  • Each color represents a different attribute
  • The length of the bar indicates the amount of points given to that candidate

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.

In today’s allocation system, some attributes define allocation classifications. Meaning, if candidates have one of those defining attributes—for example, if they are a prior living donor, or have a very rare blood type—then they receive absolute priority over otherwise similarly-situated candidates.

In the new continuous distribution framework, each attribute will have a specific weight, meaning some attributes will have more effect than others on the total score, yet no one attribute will decide an organ match. A candidate’s total score will determine their prioritization on the match run.

The community is invited to participate in collaborative exercises to determine how attributes are weighted and prioritized.

Making informed decisions about weighting attributes will be an important part of the continuous distribution policy development process. As each organ type moves toward continuous distribution, the community will be invited to participate in a collaborative exercise using a method called the Analytic Hierarchy Process, or AHP, to help determine how attributes are weighed and prioritized in the new framework.

Developing the new system: Working together

Many decisions have to be made, involving multiple stakeholders and comprehensive research, to develop the new system and achieve improvements for the entire donation and transplantation community. Each organ-specific committee will move through the steps below to develop a policy proposal that will open for public comment and be submitted to the Board for final approval.

Process to move each organ type to continuous distribution

Community input is being used through each phase of development to inform evidence-based rules for the new system. Here are the steps we’ll take:

Specific attributes labeled in boxes in a line next to each other separated by arrow signs. Identify attributes, build framework, modeling and analysis, public comment on policy proposal, board approved, policy implemented. Mobile image. Specific attributes labeled in boxes in a line next to each other separated by arrow signs. Identify attributes, build framework, modeling and analysis, public comment on policy proposal, board approved, policy implemented. Desktop image.

Identify attributes

For each organ type, each of the above attributes will be considered uniquely with regard to each candidate, who will receive points that are calculated into an overall score. We start by looking at how candidates are currently grouped and prioritized for organ allocation.

Build framework

The next step is to convert the organ type’s existing allocation policy into the new framework. The OPTN is using several different methodologies to develop these frameworks. Depending upon the organ, this can include a combination of the following steps:

  • Align attributes: Each attribute is aligned with one of the five goals mentioned above that are in alignment with NOTA and the Final Rule. We then use clinical data to compare attributes with similar goals.
  • Prioritize attributes against each other: The specific weight of each attribute determines how much influence each attribute will have toward the overall score. This step can include any of the following analyses:
    • Community input is being collected through a method called the Analytic Hierarchy Process or AHP. The AHP exercise shows each participant a pair of attributes that will be used to prioritize candidates. The participant must decide if all else is considered equal, which attribute is more important than the other when prioritizing a candidate for an organ. Learn more about AHP.
    • A revealed preference analysis to review how multiple decisions have been made in the existing organ allocation system. For example, how important was distance compared to waiting time when a decision was made between two candidates? The analysis will take the current system and create a baseline to be measured against.
      Read: revealed preference analysis for lung
    • Mathematical optimization to help identify ideal trade-offs between different attributes.
  • Convert attributes into points: For each attribute that will be considered toward the overall score, a decision will be made about how to assign points to candidates according to differences in the attribute. For example, how many points do we give to blood type A versus O? 100 miles versus 1,000 miles?
  • Conduct sensitivity analysis: A sensitivity analysis is an analysis used to measure the impact of a change to a single variable. For example, if a change is made to the weight of any attribute, the new match run will be shown as the outcome. Sensitivity tools will be built for each organ type to evaluate continuous distribution and will be made publicly available as part of the development process.
    Explore the lung sensitivity tool

Modeling and analysis

Scientific Research and Transplant Registry (SRTR) modeling and results: The SRTR will take proposed allocation policies and model them to determine the impact on candidates. These results will be produced in a report to help identify any potential unintended consequences or harmful outcomes for these example groups. These results will estimate the benefit of the new proposal and inform any needed improvements.

Public comment on policy proposal

Considering community input, modeling and analysis, and committee project work, propose a new composite score as a policy proposal for public comment. See details around the policy development process, including public comment.

Board approval

After the Board of Directors approves the proposal with the new framework, plans for implementation begin.

Implementation

As each organ moves into continuous distribution, implementation of the approved policies is projected to take approximately 12 months due to the range of changes, required education to the community, and expected impact.

NEW SYSTEM DEVELOPMENT: Progress by organ

The continuous distribution framework will be flexible enough to apply to all organ types. Using the same framework for all organs will improve organ allocation by creating consistency and transparency for the entire transplant community.

The current organ matching process is different for each organ type. To develop a framework that works for each organ, each organ type will be looked at individually. This process started with lung and is continuing with kidney and pancreas.

Organ Expected start
Lung January 2019
Kidney and pancreas June 2020
Liver December 2021
Intestine December 2021
Heart January 2023
Vascularized Composite Allograft January 2023
Get involved

Take action and help build the framework

Continuous distribution is the future of organ allocation. Your input is critical to the process, and supports the development of a consistent framework that is best for patients and for the donation and transplantation community.

The entire community has the opportunity to participate in the development of continuous distribution in several ways.

  • Add your voice to public comment, which happens twice a year and is an essential part of the policy development process.
  • Continuous distribution is also discussed at regional meetings.
  • Participate in prioritization exercises that use a method called the Analytic Hierarchy Process (AHP).

AHP prioritization exercises

AHP is being used to inform the development of the framework for each organ type through prioritization exercises. The AHP process asks participants to compare two attributes against each other and select their level of importance when considering a candidate for organ transplant. This information will be used to inform the weight of each attribute to the overall score.

Video: Introduction to prioritization using Analytic Hierarchy Process

Learn more about the analytic hierarchy process, and how to participate in prioritization exercises.

We encourage all members of the donation and transplantation community, including donors, patients and their loved ones, to participate in these important exercises.

Each organ type will have an AHP exercise. These AHP exercises will be used to inform each organ committee as they move through the process of developing frameworks for each organ type.

Organ AHP exercise
Lung Was open during summer 2020 public comment and closed on Oct. 1, 2020.
Kidney Was open during winter 2022 public comment and closed on March 23, 2022.
Pancreas Was open during winter 2022 public comment and closed on March 23, 2022.

This method was chosen because it has been used effectively by other health care groups to involve patients in making clinical decisions.

Background & resources

In December 2018, the OPTN approved a continuous distribution model as a framework for developing future organ allocation policy, upon the recommendation of a specially called Ad Hoc Geography Committee. Continuous distribution was selected after consideration of multiple alternative frameworks and was developed with input from the public and the transplant community. Recent changes to organ allocation have been made in an effort to align with this new framework and improved equity in organ allocation. Visit the Ad Hoc Geography Committee page for more information about their recommendations.

Glossary

Allocation

The process of determining how organs are distributed. Allocation includes the system of policies and guidelines that ensure that organs are distributed in an equitable, ethical and medically-sound manner.

Allocation policies

Rules established by the OPTN to guide and regulate organ allocation and distribution in the U.S.

Analytic Hierarchy Process (AHP)

A multi-criteria decision-making methodology. The OPTN is using AHP to help gather information for the development of continuous distribution. Participants in AHP exercises are asked to make decisions about the relative importance of organ attributes when compared to each other.

Attribute

An attribute is a quality or characteristic of something. In organ allocation, attributes are criteria used to classify and sort and prioritize candidates. For example, in lung allocation, attributes include medical urgency, travel mode, ischemic time, blood type compatibility, and others. Each organ type will have its own attributes in continuous distribution.

Candidate

A person registered on the organ transplant waiting list.

Classification-based framework

A classification-based framework groups similar candidates into classifications or groupings. Candidates are then sorted within those classifications. A candidate will only appear in the classification that is most beneficial to them. This is the framework currently used to allocate organs.

Cold Ischemic Time

The amount of time an organ spends being preserved after recovery from the donor.

Composite Allocation Score

A composite allocation score combines points from multiple attributes together. Continuous distribution uses composite allocation scores in a points-based framework.

Distribution

The way something is shared across a group or area.

Framework

The collection of policies and procedures used to distribute organs. Examples include concentric circles and continuous distribution.

Match run

A computerized ranking of transplant candidates based on donor and candidate medical compatibility and criteria defined in OPTN policies.

Points-based framework

A points-based framework gives each candidate a score or points. Organs are then offered in descending order based on the candidate’s score. Continuous distribution of organs involves a points-based framework.

Weight

Weights are the relative importance or priority of each attribute toward our overall goal of organ allocation.