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Continuous Distribution

About

The Organ Procurement and Transplantation Network is working to develop a more equitable system of allocating deceased donor organs. The new approach, continuous distribution, will provide organ offers by considering many factors that contribute toward a successful transplant, at once.

This new framework will dissolve hard boundaries that currently exist in the classification-based system and be flexible enough to apply to all organ types. The donation and transplantation community is working together through research and analysis to design this framework to determine patient priority in the match run.

The current classification-based system gives points to candidates at various steps of a sequence. When 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.

Continuous distribution will change organ allocation from placing patients into rank-ordered classifications for consideration, to considering all candidates at the same time. Candidates will be ranked with an overall score that is determined by considering multiple patient factors, “attributes”. This overall score includes not only medical urgency and patient outcomes, but also factors such as candidate biology and efficiency of organ transport.

Example of current classification-based system

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.

The four candidates in this broad example, A, B, C and D, vary in terms of medical urgency, distance from the donor hospital, candidate biology (compatibility) and predicted one-year post-transplant survival.

In the current classification system, one of these factors could determine a particular order in which a candidate is prioritized in the match run.

For example, based solely on distance, candidate C would receive an offer first, followed by A, B and D. If priority is given to medical urgency, candidate B would receive the first offer, followed by A, D and C.

Continuous distribution is intended to weight all factors together to determine offer order. Depending on the formula chosen, candidate B 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. Depending on the weighting of factors, the remaining order 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.

Goals of the new continuous distribution framework are consistent with allocation requirements in the OPTN Final Rule:

  • 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
  • Consider resource requirements for procuring and transporting organs

The new points system

Attributes related to the overall score include medical urgency, expected post-transplant outcome, candidate biology, patient access and efficiency of organ placement.

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. 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.

A higher score puts a patient closer to the top of the waitlist and more likely to receive an organ transplant.

Attributes and the goals they support

Image organized into a table format with each attribute belonging to a specific goal. Attributes 1 year survival without transplant and pediatric age group belong to the goal to prioritize sickest candidates first to reduce waiting list mortality which is identified as Medical Urgency. Attributes q year survival with transplant and pediatric age group belong to the goal to prioritize candidates who are expected to survive for at least one year after receiving a transplant which is identified as Post-Transplant survival. Attributes blood type, sensitization, and candidate size belong to the goal to increase transplant opportunities for patients who are medically harder to match which is identified as Biologic Match. Attributes prior living donor and pediatric age group belong to the goal to increase transplant access for patients under the age of 18 and patients who have previously donated an organ or part of an organ which is identified as Patient Access. Attributes travel efficiency and proximity efficiency belong to the goal to consider resource requirements required to match, transport, and transport, and transplant an organ which is identified as Placement Efficiency. Image organized into a table format with each attribute belonging to a specific goal. Attributes 1 year survival without transplant and pediatric age group belong to the goal to prioritize sickest candidates first to reduce waiting list mortality which is identified as Medical Urgency. Attributes q year survival with transplant and pediatric age group belong to the goal to prioritize candidates who are expected to survive for at least one year after receiving a transplant which is identified as Post-Transplant survival. Attributes blood type, sensitization, and candidate size belong to the goal to increase transplant opportunities for patients who are medically harder to match which is identified as Biologic Match. Attributes prior living donor and pediatric age group belong to the goal to increase transplant access for patients under the age of 18 and patients who have previously donated an organ or part of an organ which is identified as Patient Access. Attributes travel efficiency and proximity efficiency belong to the goal to consider resource requirements required to match, transport, and transport, and transplant an organ which is identified as Placement Efficiency.

Medical Urgency: Amount of risk to a candidate’s life or long term health without receiving an organ transplant.

Post-Transplant Survival: A candidate’s likelihood of survival for one year after receiving a transplant.

Candidate Biology: Medical characteristics of a candidate can make them harder to match. This can include a candidate’s blood type, their body’s sensitivity to accepting an organ, or their height.

Patient Access: This addresses transplant access for candidates under the age of 18, as well as prior living donors, those who have previously donated an organ or part of an organ.

Placement Efficiency: The amount of resources required to identify a suitable candidate willing to accept the organ and deliver the organ for transplant.

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 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.

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. The total score will determine a candidate’s position on the waitlist.

In today’s allocation system, some attributes define allocation classifications. Meaning, if candidates have one of those defining attributes, they receive absolute priority over otherwise similarly situated candidates. To inform the decisions about an attribute’s weight, the community is invited to participate in an exercise using a method called the Analytic Hierarchy Process, or AHP.

Take action on this page to participate today.

Developing the Framework

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.

Community input is being used through each phase of development to inform evidence-based rules for the new system.

Flow chart that has a series of boxes as steps with an action inside each box. From first to last: identify attributes, categorize attributes, prioritize attributes against each other and convert attributes into points, build framework, modeling and analysis, public comment on policy proposal, board approval and the beginning of implementation. Flow chart that has a series of boxes as steps with an action inside each box. From first to last: identify attributes, categorize attributes, prioritize attributes against each other and convert attributes into points, build framework, modeling and analysis, public comment on policy proposal, board approval and the beginning of implementation.

Lung is the first organ type to work through the process. Progress to date and decisions remaining for lung are below.

Decisions that have been made

  1. Identify attributes
    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.

Decisions and steps remaining

  1. Assign values
    • Prioritize attributes against each other
      The relative weight of each attribute determines how much influence each attribute will have toward the overall score. This step has two parts:
      • Review and analyze results of the AHP exercise from OPTN committees and the broader community
      • Compare to “current state” through a revealed preference analysis. A revealed preference analysis involves looking at mathematical trends in order to review how multiple decisions have been made. 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.
    • 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?
  2. Build framework
    • Develop the composite score
      The composite score will be a combination of decided weights and rating scales.
    • Conduct sensitivity analysis
      A sensitivity analysis is an analysis used by statisticians to change a single variable slightly in order to measure the impact on an outcome. For continuous distribution, a sensitivity tool has been built to evaluate continuous distribution of lungs. For example, if a change is made to the weight of any attribute, the new match run will be shown as the outcome.
  3. 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.
  4. 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, here.
  5. Board approval
    After the Board of Directors approves the proposal with the new framework, plans for implementation begin.
  6. Implementation
    Implementation of the policy for lung allocation is projected to take approximately 12 months due to the range of changes, required education to the community, and expected impact.

Roadmap

The adopted 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, starting with lung.

OrganStart
Lung Winter 2019
Kidney Spring 2020
Pancreas Spring 2020
Liver Winter 2021
Intestine Winter 2021
Heart Winter 2023
Vascularized Composite Allograft Winter 2023

Take Action

A method called the Analytic Hierarchy Process (AHP) is being used to inform the development of the framework through a prioritization exercise. You are invited and encouraged to participate in this exercise. AHP 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.

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

Participate in the exercise

Submit your interest by completing this short form. You will receive an email to create an account and participate in the exercise within 72 hours of submitting. Your input is critical to the process and will support the development of a framework that is best for the donation and transplantation community.

Video about the AHP prioritization exercise

We encourage all members of the donation and transplantation community to participate in this important exercise.

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.

Alexandra Glazier, J.D., M.P.H., President and CEO of New England Donor Services and a member of the Ad Hoc Geography Committee, describes the legal and regulatory history and perspective for organ distribution in the United States, as well as recent legal developments that may influence how current and future organ distribution policy is interpreted.