Evolution of out-of-sequence liver allocation, 2019-2024

Allocation out-of-sequence (AOOS) refers to deviation from the match run order in deceased donor organ allocation and is intended for use in exceptional cases to expedite organ placement. Contemporary patterns of AOOS in liver transplantation are not well characterized. This study aimed to describe liver AOOS practices and examine their association with organ utilization. Liver match runs from 2019 to 2024 were analyzed using the Organ Procurement and Transplantation Network potential transplant recipient data set to identify AOOS events. Data from the Scientific Registry of Transplant Recipients were incorporated to analyze program- and Organ Procurement Organization (OPO)-specific organ utilization and offer acceptance. AOOS prevalence, timing, and geographic variability were examined, and correlations with adjusted utilization metrics were assessed. AOOS increased from 5% in 2019 to 18% in 2024, with use concentrated in a subset of OPOs (range, 2%-39%; median, 17%) and centers (range, 0%-55%; median, 10%), often in shared geographic areas. From 2019 to 2024, AOOS offers were initiated progressively earlier in the allocation process. OPO-level AOOS use was not correlated with donor yield, though center-level AOOS acceptance was associated with higher adjusted offer acceptance. These findings highlight a potential need for further standardization of AOOS practices in liver transplantation.