Liver Transplant System's Attempt to Correct Sex Bias Shows Mixed Results

The United States liver transplant system has implemented a revised scoring model, MELD 3.0, intended to address historical sex-based disparities in organ allocation. While early data suggests the update has temporarily increased transplant rates for women, the gains have not been sustained, indicating that the system's complexities, particularly regarding organ size, continue to pose challenges.

Historically, the Model for End-Stage Liver Disease (MELD) score has been used to prioritize patients awaiting liver transplants, with higher scores indicating greater urgency. However, the original MELD system inadvertently underestimated the severity of illness in women. A key factor was the use of creatinine levels, a waste product filtered by the kidneys. Women typically have lower muscle mass than men, leading to lower creatinine levels even with comparable kidney dysfunction. This difference could result in women receiving lower MELD scores, placing them lower on the waitlist.

A 2020 study revealed that women were significantly less likely than men to receive a deceased donor liver transplant and more likely to die while waiting.

Introducing MELD 3.0

In 2023, Dr. Ray Kim, who developed the original MELD system, introduced MELD 3.0. This updated model incorporates several changes, including adjusting scores by 1.33 points for women to account for differences in creatinine levels due to muscle mass. The model also includes additional biomarkers like albumin and accounts for interactions between variables.

Researchers estimated that MELD 3.0 could prevent approximately 20 waiting list deaths annually, a significant figure given that around 800 liver transplant candidates died while waiting in the previous year.

Persistent Disparities: The Size Factor

Despite the improvements, MELD 3.0 has not fully resolved the equity issue. Experts point to body size as a second major factor contributing to disparities. A donated liver must physically fit within the recipient's body. Since women are typically smaller than men, they may be less likely to receive a liver that is a suitable size, even if they have a high MELD score. Conversely, a smaller liver may not pose a problem for a larger recipient.

Sommer Gentry, a professor at NYU Grossman School of Medicine and contributor to the MELD 3.0 paper, explained that the smaller a patient is, the less likely they are to be offered a liver that will work for them. This means women often wait longer for a compatible organ.

Evaluating MELD 3.0's Impact

Initial analyses of MELD 3.0's implementation showed a temporary increase in liver transplant rates for women. However, an analysis of nearly 10 million records from over 60,000 candidates found that this boost was short-lived. Within 15 months of the new model's adoption, women's transplant rates drifted back to pre-MELD 3.0 levels. While women received more organ offers under MELD 3.0, suggesting their scores more accurately reflected their sickness, they were not necessarily receiving those organs, likely due to size mismatches.

Authors of the study suggest that revising MELD criteria alone may be insufficient if body size remains a significant barrier. They argue that the focus should shift from sex as a proxy to addressing the lack of allocation systems that ensure patients with smaller body sizes have equitable access to appropriately sized livers.

Moving Toward Greater Equity

Experts believe that incorporating body-size considerations into organ allocation could have broad benefits, potentially improving equity not only in liver transplants but also in heart and lung transplants where organ size is critical. A system that prioritizes organ fit alongside patient urgency could ensure smaller candidates receive viable organs suited to them, rather than waiting for a liver that might fit but is otherwise less ideal.

Implementing such a system would require approval from the Organ Procurement and Transplantation Network. Further research is needed to develop and validate these new allocation strategies. The challenges faced in liver transplantation echo broader issues in healthcare, where medical standards, often based on averages, can inadvertently disadvantage certain groups, including women and racial minorities.