Scoring System Could Mean Better Access to Lung Transplant

The organ transplantation field has seen many advancements over the years, with lung transplant rates showing an upward trend.

Consider the statistics. Since 2011, there has been a 148.3% increase in lung transplant rates, reaching more than 258 transplants per 100 patient-years according to the Scientific Registry of Transplant Recipients. US hospitals performed 2743 lung transplants in 2022 and 3049 in 2023, representing the highest number of lung transplants ever, says Maryam Valapour, MD, MPP, pulmonologist at Cleveland Clinic.

Still, more than 4200 adult patients are on the lung transplant waitlist in the United States, a steady count that has been observed since 2011. Opportunity remains to improve access for hard-to-match candidates due to biological factors such as height and blood type.

Introducing an Alternate Scoring System

Valapour, with researchers at Cleveland Clinic and Case Western Reserve University, both located in Cleveland, Ohio, teamed up to design and validate a new scoring system that could enhance equity in organ transplantation, increase transplant rates, and improve survival. Their alternative scoring system hones in on blood type and height — two characteristics that are biological disadvantages within today’s Composite Allocation Score (CAS).

The alternate scoring system uses empirical models to generate a candidate’s expected daily donor supply given their diagnosis and unique combinations of height and blood type. “Daily donor supply is inversely related to biological disadvantage, so we transformed it to a point scale that could be used in the CAS calculation to represent how difficult or easy it would be for a candidate to access a transplant,” said Valapour, who is the co–senior author of this research.

Next, the team performed simulation analyses using the Computational Open-source Model for Evaluating Transplantation (COMET) to examine the possible impact of adopting this score for the lung transplant population. COMET starts with creating “realistic synthetic populations of organ donors and lung transplant candidates,” based on data across the United States, explained Johnie Rose, MD, PhD, scientist from Case Western Reserve University and co–first author.

“It then allows us to simulate the impact of different allocation rules on important outcomes like transplant volume, deaths on the waiting list, and posttransplant survival.”

How the Proposed Model Differs

The Supply-Adjusted CAS looks to solve current allocation rules in the CAS that lead to inequities for candidates for lung transplants.

“Our lung transplant physician team members observed that the current point system, designed to assist patients facing biological challenges to accessing a transplant, was insufficient for certain groups,” Valapour said.

Part of the issue is how the CAS weighs the effects of blood type and height independently. Instead, the research team’s proposed approach considers blood type and height-based disparities simultaneously, offering a more holistic view of biological disadvantages.

“Our approach assigns points in a way that directly reflects the supply of donor organs for each candidate based on the combined effects of their unique height and blood type combinations,” Valapour added.

Subsequently, simulation modelling enabled the researchers to “compare the existing scoring scheme implemented in lung transplant policy today to an alternative policy that replaces points assigned to height and blood type with points derived from our supply-based scoring algorithm,” Valapour added.

As a result, they project that transplant volume would rise, and waitlist deaths would fall under the hypothetical rule change.

Addressing Inequities

Lung transplant candidates indeed need to match donors of similar height and compatible blood type. As the researchers investigated these biological factors, however, they found that shorter candidates were not receiving as many transplants as taller candidates. Size is a vital factor as lung transplant candidates require donor lungs that are appropriately sized for their height and will fit within their thoracic cavity.

“A candidate who is 5’9” has a 61% higher likelihood of accessing a transplant compared with a candidate who is 5’3,” Valapour explained. “This issue is especially pronounced for women who tend to be shorter than men (eg, 25% of women in the US are under 5’3”, compared to only 1% of men). Height disparity is a central mechanism for the long-observed sex disparity in lung transplantation.”

Another potential disadvantage is blood type. Candidates with type-O blood can only accept organs from type-O donors, while type-O organs are compatible for candidates of any ABO blood type. Controlling for height and patients’ medical urgency, the researchers found that type-O candidates had a 37% lower rate of transplant compared with type-A candidates under the current system. “This means that type O candidates face the unique challenge of having to compete with candidates of all blood types for scarce organs,” Valapour added.

Height and blood type are pieces of a larger discussion around what it means to provide equitable healthcare, which traditionally focuses on disparities across sex, race, and socioeconomic status. “Our scoring system aims to mitigate the compounded biological barriers that candidates face in accessing transplantation, bringing us closer to the goal of ensuring that equally sick candidates have equal access to transplantation,” Valapour said.

“Additionally, this supply-based scoring approach may help rectify the longstanding inequities in lung transplantation access for women in the United States, fostering a fairer system for all candidates.”

Advocating for Scientifically Validated Solutions

The research team’s engagement in clinical practice, policymaking, and research within lung transplantation allows for a holistic understanding of the field.

Next, the researchers will present this analysis as an alternative scoring system to be considered for US lung allocation system, Valapour said. “We will continue to investigate ways to enhance our understanding of risk and outcomes including the effects of delays in accessing a transplant with the ultimate goal of improving timely access and survival of lung transplant patients.”

This project was funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health (R01HL153175).

Valapour and Rose had no financial conflicts to disclose.