Out of Sequence Liver Transplants: A Nationwide Analysis of Organ Utilization and Allocation Equity

Introduction: Deceased donor liver allocation typically follows a ranked matchrun of potential recipients, but organ procurement organizations (OPOs) may deviate in exceptional circumstances with "out-of-sequence" (OOS) matches.We aimed to evaluate trends and factors associated with OOS matches.Methods:All donor match-runs in the U.S. (1/1/2013-12/31/2023) from the Potential Transplant Recipient (PTR) data were analyzed.OOS allocations were identifi ed by bypass reasons: (861) Operational OPO, (862) Donor medical urgency, (863) Off er not made due to expedited placement.A hierarchical mixed-eff ects model with transplant centers (TCs) nested in OPOs was used to assess factors associated with OOS allocation.Results:From 2013 to 2023, there were 93,409 liver transplants (LTs), 4,792 (5.1%) were OOS allocations.Over time, the percent of LTs resulting from OOS matches increased from 2.0% (n=135 of 6703) in 2013 to 11.0% (n=770 of 6993) in 2023 (Figure 1A).Nearly one-quarter of OOS LTs (24.5%, n=1,172) occurred at fi ve TCs and just over a quarter of OOS liver transplants were allocated from fi ve OPOs (25.8%, n=1237).There was signifi cant variation in use of OOS LTs between TCs (minimum: 0.1% (n=1 of 588), maximum: 21.2% (n=134 of 631)) and OPOs (minimum: 0.9% (n=13 of 1449), maximum: 13.9% (n=134 of 960)); Figure 2.This variation in OOS LT rate was not correlated with OPO organ utilization rate (R 2 <0.01),OPO LT volume (R 2 =0.02), or TC LT volume (R 2 =0.07) (Figure 1B-D).On hierarchical mixed eff ects model, White recipients (OR 1.21, 95% CI 1.05-1.42)and recipients from socially advantaged neighborhoods (SVI>0.8,OR 1.12, 1.02-1.23)were more likely to receive OOS LT despite controlling for confounding allocation factors (Table 1).The conditional and marginal R 2 were 0.548 and 0.256 respectively, indicating ~53% of the explained variation in OOS use was secondary to OPOs and TC practices, rather than donor or recipient factors.Conclusions:OOS LTs are increasingly frequent, with signifi cant variability across OPO's and TCs.OOS were not correlated with increased organ utilization at an OPO-level but were associated with disparities in race and socioeconomic status, emphasizing the need for equitable OOS allocation practices.