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Liver transplant waitlist candidates who are smaller in size are significantly less likely than larger candidates to receive a liver transplant, contributing to a sex disparity in organ transplants, according to a retrospective study.

After candidates were categorized into six groups according to body surface area (BSA) from smallest (group 1) to largest (group 6), it was found that with each increase in group number, waitlist time decreased (234 days for group 1 vs 179 days for group 6, P<0.001), reported Catherine E. Kling, MD, MPH, of the University of Washington in Seattle, and colleagues.

In addition, the proportion of the group undergoing transplant also improved (46% in group 1 vs 57% in group 6, P<0.001), they noted in .

The smallest two groups were disadvantaged under the current allocation model, with 37% and 7.4% fewer livers allocated relative to their proportional representation on the waitlist, Kling and team said.

Of note, among the smallest two BSA groups, 84% and 61.1%, respectively, were female.

"Small size, measured in this study by BSA, affects liver allocation for both male and female candidates, but it disproportionately disadvantages female candidates, who are more likely to be small," Kling and colleagues wrote.

"It is very easy to find an appropriate-sized liver for large candidates on the waitlist, but small candidates seem to wait longer, even if they are at the top of the list," Kling told 番茄社区app in an email.

However, the researchers found that a simulated "novel allocation policy" that distributed livers from the smallest 10% of donors by BSA to the smallest 15% of waitlist candidates resolved the disparity, as did a model that would split livers from three larger groups of donors by BSA into the smallest two groups.

"We showed that by splitting all livers acceptable by Organ Procurement and Transplantation Network (OPTN) criteria, the size disparity could be overcome," Kling and colleagues wrote. "However, this is likely an overestimate of the true impact because splitting a liver requires surgical expertise that not all centers have, as well as additional staffing for 2 recipient teams."

The researchers also found that smaller waitlist candidates had lower Model for End-Stage Liver Disease (MELD) scores, which -- along with donor blood type and location -- is considered when allocating liver transplants. Higher MELD scores indicate a higher risk of death, and therefore more urgency. MELD scores take into account various liver markers, including serum creatinine, which can be higher in men because of their generally higher proportion of muscle mass.

"While MELD-based allocation was successful in improving waitlist mortality, studies have consistently demonstrated that female patients are disadvantaged at every step of the process, including access to listing and worse outcomes once on the liver transplant waiting list, with implicit bias likely contributing," Kling and team wrote.

has shown that livers that are too small or too large for recipients can result in poorer transplant outcomes, noted Angela L. Hill, MD, and William C. Chapman, MD, both of Washington University in St. Louis in Missouri, in an . "The study is both important and timely given the ongoing obesity epidemic and likely increasing proportion of larger stature donors," they wrote.

However, they added, although BSA is better than height for predicting liver size, it doesn't account for "other aspects of a patient's body habitus known to affect liver size."

BSA is calculated by height and weight. Patients on liver transplant waitlists may be more likely to have sarcopenia and ascites, conditions from cirrhosis that could affect BSA. "Incorporating more detailed recipient information would appear necessary, such as image-based volumetrics, especially because these data should be readily available to the accepting transplant team," Hill and Chapman wrote.

The study would have been better served if an upcoming revised version of the MELD score had been incorporated into the model, they noted. MELD 3.0 includes a covariate for female sex.

However, Kling told 番茄社区app that "introducing MELD 3.0 may help small candidates move up the list, but it won't necessarily get them increased access to the small donors, which is what we need to do to overcome the disparity we see."

For this study, Kling and co-authors used data for all adult candidates on the Organ Procurement and Transplantation Network (OPTN) liver waitlist from June 2013 to March 2020. They included 84,201 waitlist candidates (median age 57), of whom 36.2% were women.

For the donor dataset, they reviewed all deceased liver donors whose livers were allocated and transplanted during the same period, excluding donors allocated to children. They included 41,341 donors (median age 42), 39.9% of whom were women.

Kling and colleagues found that of the several novel allocation models, the one that appeared "most equitable" was the one that allocated the smallest 10% of donors by BSA to the smallest 15% of recipients, with 36.8% of livers donated to female candidates.

The researchers noted several limitations to their study, including the fact that the presence of ascites in a candidate, which would increase a recipient's BSA and decrease the donor-to-recipient BSA ratio, is not recorded in the OPTN database and therefore is not included as a separate factor in the BSA models.

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