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Standardize Six Minute Walk for Lung Allocation

eye iconAt a glance

Current policy

Six-minute walk distance factors into the lung composite allocation score (CAS). The distance (measured in feet) that a lung candidate can walk in six minutes factors into both the medical urgency and post-transplant outcome portions of the lung CAS. OPTN Policy does not include specifics on conducting these tests, so how these tests are performed varies among programs. This proposal includes a policy change, a guidance document, and data definition changes.

Supporting media

View presentation PDF link

Proposed changes

  • Policy change:
    • Require lung transplant programs to perform an oxygen titration test prior to a patient’s first six-minute walk test
  • Guidance:
    • Creates a guidance document for lung transplant programs to help supplement clinical guidelines
  • Data definition changes:
    • Update the six-minute walk distance data definition to match the policy changes and guidance

Anticipated impact

  • What it's expected to do
    • Provide guidance to create more consistency between programs in how the six-minute walk is conducted
  • What it won't do
    • Change how the six-minute walk impacts the CAS
    • Create a policy that outlines exactly how to conduct the six-minute walk

Terms to know

  • Six-minute Walk Test: A test that helps assess a lung transplant candidate’s cardiopulmonary function. The patient is asked to walk as far as they can in six minutes.
  • Composite Allocation Score (CAS): A composite allocation score combines points from multiple attributes together. The score determines a candidate’s place on the match run.
  • Oxygen Titration Test: A test to evaluate a patient’s oxygen needs when at rest and during exercise.

Click here to search the OPTN glossary


Read the full proposal (PDF)

eye iconComments

UC San Diego Health Center for Transplantation | 03/20/2024

UCSD Center for Transplantation (CASD) appreciates the thought and effort that the Lung Transplantation Committee put into the development of the proposal to Standardize Six Minute Walk for Lung Allocation as well as the opportunity to comment. While we understand and support the Committee's efforts to standardize practice, as written the proposal does not stipulate whether this a explicitly a rest/exercise test performed by the pulmonary function lab or a 3-minute step test that can be conducted in the clinic, similar to what is allowable for DME companies to supply supplemental oxygen.

Although the committee states that it has a low financial impact on the transplant hospitals, it is not mandating that transplant hospitals provide the needed support. This places the transplant programs at a major disadvantage given cost containment that is being looked at by both payors and hospital organizations.

Given the estimate is roughly 240 hours of OPTN time and resources needed to implement this proposal by providing education, guidance, and communication efforts to transplant hospitals with lung transplant programs - it should be noted that this estimate (as is true with all proposals) does not account for the time and resources that individual programs must put forth to communicate the potential changes, provide education, develop new practices and related guidance. This is a significant burden to the programs with minimal added benefit.

Calvin Henry | 03/19/2024

I generally support this proposal. Although the proposal didn’t note an additional fiscal burden on the transplant center or labs, there is an additional burden placed on the patient that should be recognized. As a former lung candidate, I would recommended that oxygen titration take place on a separate day than a 6MW as it is very physically demanding for a significant number of candidates pre-transplant. If arterial gas pull is also required as part of the titration, needs of a candidate under the age of 12 may need to be considered as that pull/s can be painful. Also, candidates are supported by their families and additional accommodations, especially those from underserved communities, may be needed so that the extra appointments can be made.

I strongly support the standardization aspect of this and urge further clarity to address recommended oxygen saturation (80?, 85?, 88?) so that a candidate can continue the 6MW as that is open to variability.

International Society for Heart and Lung Transplantation | 03/19/2024

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Duke University Hospital | 03/19/2024

We support the updated UNOS Six-Minute Walk Test (6MWT) policy and in the UNOS Working Group’s goals of defining terms more specifically to create more consistency between transplant programs in how the 6MWT is performed. Hopefully this will result in less programmatic variability and “gaming” of the system for more equitable scoring across patient candidates.

While this is a welcomed positive step forward, we encourage the UNOS Lung Committee and the lung transplant community to take this effort further as the current policy stops short of achieving more potential benefits for our patients. The policy statement acknowledges “in the current allocation score (the lung CAS), the six-minute walk distance has opposing effects in the medical urgency and post-transplant outcome scores” (p.6 of OPTN Public Comment Proposal). Both the former lung allocation score (LAS) and current CAS system are using one test, a modification of the standard 6MWT, to convey two vastly different aspects of a patient’s condition. The modified 6MWT with minimal to no oxygen is more reflective of a patient’s lung disease while the standard 6MWT with adequate oxygen to maintain saturation throughout the entirety of the test is more reflective of physical conditioning or frailty. The American Thoracic Society Guidelines for the Six Minute Walk Test describe the utility of the test as a means to measure functional capacity with the stipulation that adequate oxygen is provided.

Patients are being disadvantaged even with this updated policy as we are using one test to try to accomplish two vastly different ends. An improved 6MWT policy would be to have two separate tests: one utilizing the updated policy (using minimal oxygen as described in the proposal) that it incorporated into the Waitlist Urgency calculation and a second, more traditional 6MWT that provides enough oxygen to maintain adequate oxygen saturations throughout the duration of the 6MWT that would be incorporated into the Post-transplant Survival calculation.

As far as two tests exhausting patients, these can be performed on different days. If programs and patients are reluctant to perform both tests, then they can follow the current process with other CAS clinical variables and choose which one of the two 6MWT they want to include and accept a defaulted value for the other.

The importance of having integrity of data for equitable allocation demands this and our patients and programs deserve better.

OPTN Transplant Administrators Committee | 03/19/2024

The OPTN Transplant Administrators Committee appreciates the opportunity to comment on the OPTN Lung Transplantation Committee’s policy proposal, Standardize Six Minute Walk for Lung Allocation. The Committee recommends that concerns relating to center capacity and implementation feasibility be considered with this change, as some centers have greater access to resources than others. The Committee also recommends that more consideration be given to the ranges of distance walked, and to consider that there may need to be exceptions in the event a patient is in the ICU and cannot go to a testing facility. 

Anonymous | 03/19/2024

The oxygen titration protocol is time consuming, presents logistical complications, and will ultimately be a burden to transplant centers. We should follow ATS guidelines for 6MWT rather than creating a different approach.

Region 10 | 03/19/2024

3 strongly support, 12 support, 5 neutral/abstain, 0 oppose, 0 strongly oppose

Region 9 | 03/19/2024

0 strongly support, 4 support, 6 neutral/abstain, 0 oppose, 0 strongly oppose

Region 6 | 03/19/2024

1 strongly support, 7 support, 5 neutral/abstain, 0 oppose, 0 strongly oppose

This proposal was not discussed during the meeting, but attendees were able to submit comments. One attendee commented that there should be consideration for standardizing the six-minute walk for any organs that use this value. 

NATCO | 03/18/2024

NATCO would like to thank the Lung Transplant Committee for their time and work on Standardizing Six Minute walk for lung Allocation. Standardization to how procedures are documented and carried through is essential when caring for our transplant recipients. This allows for proper allocation prioritization along with decreasing possible inequities.

Should policy specify a timeframe within which the oxygen titration test must be completed ahead of the six-minute walk test
Completing the O2 titration test prior to the 6-minute walk is reasonable so that the patient can perform the test to the best of their ability. We also agree that having the patient perform both tests on the same day may be to taxing on the patient, therefore we support separating the test and it is reasonable to do so within a 6–12-week period with 6 weeks being ideal. For those patients that are too sick, on mechanical ventilation or ECMO, marking 0 feet is appropriate. Further consideration should also be given to those individuals who are in the hospital setting and on high flow oxygenation or ICU setting. These individuals will also not be able to perform the test and having them do this in the unit corridors could be harmful.
What, if any, consideration should be given for altitude for candidates who live at a significantly different altitude compared to the transplant hospital where they are registered?
When looking at individuals that live at higher altitudes than the transplant center of where the six-minute walk is performed could disadvantage this population if it is not identified. There should be consideration given to these patients, and it would be interesting to know if there is a standard calculation or number of feet can be identified and utilized. If not, this should be closely monitored as the proposal is rolled out so that it does not cause further disparities to this patient population.
Do you support the proposed policy requirement to perform an oxygen titration test ahead of the initial six-minute walk test for candidates at least 12 years old, and for candidates approaching 12 years of age?
Yes, we propose this for candidates at least or approaching 12 years old.
NATCO would like to thank the Lung Transplant Committee for their time and work on Standardizing Six Minute walk for lung Allocation. Standardization to how procedures are documented and carried through is essential when caring for our transplant recipients. This allows for proper allocation prioritization along with decreasing possible inequities.

Should policy specify a timeframe within which the oxygen titration test must be completed ahead of the six-minute walk test
Completing the O2 titration test prior to the 6-minute walk is reasonable so that the patient can perform the test to the best of their ability. We also agree that having the patient perform both tests on the same day may be to taxing on the patient, therefore we support separating the test and it is reasonable to do so within a 6–12-week period with 6 weeks being ideal. For those patients that are too sick, on mechanical ventilation or ECMO, marking 0 feet is appropriate. Further consideration should also be given to those individuals who are in the hospital setting and on high flow oxygenation or ICU setting. These individuals will also not be able to perform the test and having them do this in the unit corridors could be harmful.
What, if any, consideration should be given for altitude for candidates who live at a significantly different altitude compared to the transplant hospital where they are registered?
When looking at individuals that live at higher altitudes than the transplant center of where the six-minute walk is performed could disadvantage this population if it is not identified. There should be consideration given to these patients, and it would be interesting to know if there is a standard calculation or number of feet can be identified and utilized. If not, this should be closely monitored as the proposal is rolled out so that it does not cause further disparities to this patient population.
Do you support the proposed policy requirement to perform an oxygen titration test ahead of the initial six-minute walk test for candidates at least 12 years old, and for candidates approaching 12 years of age?
Yes, we propose this for candidates at least or approaching 12 years old.

Region 7 | 03/18/2024

6 strongly support, 4 support, 7 neutral/abstain, 0 oppose, 0 strongly oppose 

This was not discussed during the meeting, but attendees were able to submit comments with their sentiment. One attendee suggested that the committee should look to see if other organizations, such as AST or ASTS, have similar standards and the OPTN standards should mirror those standards. Another attendee noted that the oxygen dose test will be a considerable burden for lung programs. Lastly, another attendee added that such standardization may be helpful for abdominal organs too.

Region 1 | 03/18/2024

2 strongly support, 7 support, 4 neutral/abstain, 0 oppose, 0 strongly oppose

This proposal was not discussed during the meeting, but attendees were able to submit comments. A member commented that frailty testing needs to be standardized to be useful.

Region 5 | 03/15/2024

6 strongly support, 20 support, 10 neutral/abstain, 0 oppose, 0 strongly oppose

Region 5 supports this proposal. An attendee pointed out that it provides an objective measure of frailty for the potential recipient. But noted that if the potential recipient performs well, then they might not have as high a priority as a more frail recipient.

American Society of Transplantation | 03/15/2024

The American Society of Transplantation (AST) generally supports the proposal, “Standardize Six-Minute Walk for Lung Allocation,” and offers the following comments for consideration:

• A timeframe within which the oxygen titration test must be completed ahead of the six-minute walk test may be difficult due to logistical issues and individual patient status. Although a specific interval may not be feasible, consider adding to the guidance language that lung programs should allow adequate time for the patient to fully recover between oxygen titration and the six-minute walk test and when possible, these tests should be done on separate days.

• The guidance language should more clearly emphasize that the resting oxygen determination and titration should be reported and performed using continuous flow oxygen (as opposed to pulse delivery systems).

• Candidates who live at a significantly different altitude compared to the transplant hospital where they are listed requires additional, careful consideration. The AST recommends that the OPTN Lung Transplantation Committee assess additional altitude considerations separately to assure equity for all patients.

• Finally, while this document addresses standardization and the AST supports this approach, it should be noted that the six-minute walk test is an imperfect biomarker due to its inherent variability. As a parameter intended to reflect both severity of lung disease and extrapulmonary conditioning and as a component of both waitlist survival and post-transplant survival in the lung composite allocation score (CAS), it’s value as a biomarker for the CAS should be reexamined. Some of the risk elements reflected in the six-minute walk test and CAS components interact with one another, including variables such as functional class and resting oxygen needs. Because of this interaction, it is unclear how well the six-minute walk test further stratifies patients with reference to waitlist survival and post-transplant survival. For future consideration, the AST recommends that the OPTN Lung Transplantation Committee review this impact by evaluating potential changes that might result from removing the six-minute walk test from pre- and post-transplant survival components. Alternative variables that may more accurately and specifically address physical performance status independent of severity of lung disease should be considered in the future.

American Society of Transplant Surgeons | 03/12/2024

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Corewell Health (formally Spectrum Health) | 03/11/2024

Thank you for the opportunity to provide comments on the proposed policy to standardize the six-minute walk test (6MWT). We appreciate the work that has gone into this proposed change.

Generally, Corewell Health does not support this proposal. While we are comfortable with many of the various aspects of the proposal, we believe that it should be consistent with ATS guidelines.

More specifically, we feel the addition of a separate O2 titration study is not necessary and adds an undue clinical burden. An oxygen titration study should be performed if the 6MWT suggests that the patient may benefit from using more oxygen. The 6MWT is performed using the normal dose of oxygen that the patient is prescribed.

We would like to propose that instead all 6MWT be performed with saturation for constant monitoring for the test, saturation only be measured and documented at baseline and end of the test (consistent with ATS). If centers prefer to use continuous saturation monitoring during the walk, a handheld or finger device can be used by the patient. The test should not be terminated, however, purely based on any saturation, but rather by symptoms.

In terms of the associated guidance, we do not recommend that OPTN provide guidance separate from ATS guidelines.

If this proposed policy was adopted, we do not have concerns with the implementation timeframe and would be able to meet the September 5 date.

In terms of consideration for different altitudes, we believe the approach should be the same regardless of location.

Corewell Health supports removing the description of how the six-minute walk test should be performed from policy and instead providing more direction on how to conduct the test via guidance. We also support the proposed changes to the definition.

Region 3 | 03/11/2024

8 strongly support, 4 support, 3 neutral/abstain, 0 oppose, 0 strongly oppose

American Society for Histocompatibility and Immunogenetics (ASHI) | 03/09/2024

This proposal is not pertinent to ASHI or its members.

Anonymous | 03/07/2024

While I appreciate the need to standardize how programs perform the 6MWT, the requirement to perform formal oxygen titration tests every 6 months prior to the 6MWT has significant logistical and financial implications for both patients and transplant programs. Payers will not pay for both tests when performed on the same day. Adding O2 titration to the PFT creates strain on the PFT lab, especially if no revenue is generated to cover the costs associated with doing the test. The burdens associated with additional testing disproportionately impact rural and less financially resourced patients and can exacerbate inequities in access to lung transplant. Furthermore, without defining explicitly what constitutes on "oxygen titration test" the variability between centers will just shift from how they do the 6mwt to what they consider an oxygen titration test.

Region 8 | 03/05/2024

0 strongly support, 13 support, 4 neutral/abstain, 0 oppose, 0 strongly oppose

Anonymous | 03/04/2024

I too would like to see further clarification or exception for candidates that are undergoing urgent inpatient evaluation/listing where the completion of the current "standard" 6 MWT is difficult enough, but completion of an O2 titration study and 6 MWT would be unfeasible/unsafe. Similar to the comments by Neeraj Sinha below

"I agree with using zero feet as default for patients on ECMO and/or continuous mechanical ventilation, but please consider adding guidance for what needs to be done for a patient who is on high flow O2 and is in an intermediate care or intensive care unit. Such a patient can not safely undergo 6MWT in pulmonary laboratory, and the unit hallway is not optimal for this test: severity of disease and risk of severe desaturations, distractions, obstacles, inability to have 100 feet long obstacle-free path in an IMCU/ICU. I would suggest using "20 feet" as the default value for patients on high flow O2; as arguably the patients on high flow O2 are healthier than patients on continuous mechanical ventilation and/or ECMO where default is to assign zero feet."

Region 2 | 02/29/2024

4 strongly support, 15 support, 5 neutral/abstain, 0 oppose, 0 strongly oppose

This was not discussed during the meeting, but attendees were able to submit comments with their sentiment. One attendee noted that standardization should always be a common goal. Another attendee added that the proposal needs to be more specific about the requirements inherent in performing the oxygen titration study.

Region 11 | 02/29/2024

3 strongly support, 3 support, 11 neutral/abstain, 1 oppose, 0 strongly oppose 

Region 4 | 02/26/2024

1 strongly support, 9 support, 4 neutral/abstain, 0 oppose, 0 strongly oppose

Anonymous | 02/22/2024

I somewhat agree with standardizing the six minute walk test for lung allocation. I think the test will show who may be in greater need for a lung transplant. But, people who perform better in the test and shown to have better cardiopulmonary function than others may not have as high of priority for lung donation. Just because they may have better cardiopulmonary function doesn't mean they should potentially have lower priority.

Déboralis Ramos | 01/31/2024

Strongly Support

Neeraj Sinha | 01/26/2024

I support the proposal to standardize 6MW for lung allocation.

• Do you support the proposed policy requirement to perform an oxygen titration test ahead of the initial six-minute walk test for candidates at least 12 years old, and for candidates approaching 12 years of age? Yes

• Should policy specify a timeframe within which the oxygen titration test must be completed ahead of the six-minute walk test? Somewhere within preceding 6 - 12 weeks, ideally within preceding 6 weeks)

• If the policy change were to go into effect on September 5, 2024, would that give lung transplant programs adequate time to prepare for implementation? Yes

• Are the data definition changes clear, and would you recommend any changes? Yes and no.

• Is the guidance clear, and would you recommend any changes? No, and yes

I agree with using zero feet as default for patients on ECMO and/or continuous mechanical ventilation, but please consider adding guidance for what needs to be done for a patient who is on high flow O2 and is in an intermediate care or intensive care unit. Such a patient can not safely undergo 6MWT in pulmonary laboratory, and the unit hallway is not optimal for this test: severity of disease and risk of severe desaturations, distractions, obstacles, inability to have 100 feet long obstacle-free path in an IMCU/ICU. I would suggest using "20 feet" as the default value for patients on high flow O2; as arguably the patients on high flow O2 are healthier than patients on continuous mechanical ventilation and/or ECMO where default is to assign zero feet.

• Does this proposal strike the right balance between promoting data quality for the six-minute walk distance and managing burden on lung candidates and lung transplant programs? Yes

• What, if any, consideration should be given for altitude for candidates who live at a significantly different altitude compared to the transplant hospital where they are registered? Some consideration should be given. By gestalt: Addition or reduction of O2 flow by 1 l/m can be done for every 750 m increase or decrease in elevation respectively between oximetry study and 6MWT locations.

Samuel Kirton | 01/23/2024

I am not clear how this is different from the current standard described in ICD 94618. Are you prescribing something that is not in the ICD? If not, would it be simpler to have the centers work to the billing standard required under the ICD?