Allocation Out of Sequence in Lung Transplant: An Analysis of the UNOS Registry.

Importance: Allocation out of sequence (AOOS) allows organ procurement organizations (OPOs) to offer organs outside of standard allocation and bypass those atop the match run. AOOS may allow OPOs to successfully place medically complex organs; however, increasing use of AOOS also raises concern for inefficiencies within the allocation process and may exacerbate systemic inequities. Objective: To characterize patterns of lung AOOS among organ procurement organizations and transplant centers and compare lung transplant characteristics and outcomes between in-sequence and AOOS groups. Design, Setting, and Participants: In this retrospective cohort study, the United Network for Organ Sharing registry was queried for lung transplants performed between September 1, 2021, and June 30, 2024. Data were linked to the Potential Transplant Recipient file to identify all offers for included donor lungs. These data were analyzed from October 2024 to February 2025. Participants included adult donors who donated at least 1 lung for transplant and corresponding primary isolated lung transplant recipients. The final cohort included 7914 lung donor-recipient pairs. Exposure(s): Lung AOOS vs in sequence, defined by match-run refusal codes for donor lung offers. Main Outcome(s) and Measure(s): Donor and recipient characteristics, posttransplant outcomes, and OPO-level and transplant center-level rates of lung AOOS. Results: Overall, 7914 lung transplants were included, of which 558 used AOOS (7.1%). Rates of lung AOOS ranged from 0% to 30% among OPOs and 0% to 50% among transplant centers. Use of lung AOOS increased in the continuous distribution era (10% vs 4%; P < .001). Donors of AOOS lungs were more likely to donate after circulatory death and had lower partial pressure of oxygen/fraction of inspired oxygen ratios, longer ischemic times, and longer travel distances. AOOS recipients were less likely to require pretransplant hospitalization, intensive care, and ventilator or extracorporeal membrane oxygenation support. On multivariable analysis, lung AOOS was associated with lower odds of prolonged intubation and early acute rejection and shorter posttransplant hospital length of stay. Conclusions: AOOS is increasingly used in lung transplant and is associated with transplant of medically complex lungs into lower acuity recipients. Further investigation is needed to understand how AOOS affects lung utilization, especially in the era of continuous distribution.