To the Editor:
In the United States, organ procurement organizations (OPOs) sometimes use allocation out-of-sequence (AOOS) to place deceased donor kidneys directly with a transplant center.1, 2, 3, 4 The use of AOOS is intended to improve placement and thereby reduce the risk of organ nonuse. However, a rise in AOOS since the implementation of distance-based kidney allocation policy (KAS250) has led to regulatory scrutiny of whether AOOS is being inappropriately used in circumstances for which expedited allocation is unnecessary.1, 2, 3, 4 Published analyses describing the rise in AOOS have not accounted for the possibility that an increased difficulty in organ placement after KAS250 has led to the accumulation of more in-sequence organ offer refusals for kidneys, which might necessitate greater use of AOOS. We sought to determine whether the number of and reason for in-sequence refusals prior to AOOS initiation has changed over time.
We used data from the Scientific Registry of Transplant Recipients (see Acknowledgements) to identify all kidneys transplanted using AOOS from 2020-2024 in the United States, defining AOOS as allocations for which an AOOS refusal code appeared earlier in the match run than the eventual acceptance code. AOOS refusal codes were “861: Operational OPO,” “862: Donor medical urgency,” or “863: Offer not made due to expedited placement attempt;” refusal codes “799: Other, specify” were also identified as AOOS codes if the accompanying free-text entry contained the terms “expedited,” “aggressive,” “open offer,” or “out of sequence.”5 We calculated the median number of in-sequence offer refusals prior to the first recorded AOOS code for each AOOS-placed kidney. OPO-level median sequence number of AOOS initiation was calculated as the median of all AOOS-placed kidneys at each OPO. We also counted the frequency of each category of refusal reason for these in-sequence offers. This study was approved by the Columbia University Medical Center institutional review board. Research activities were consistent with the principles of the Declaration of Istanbul.
The proportion of OPOs performing any AOOS increased from 39% in 2020, to 86% in 2021, to 100% in 2022 onwards (Table S1). The OPO-level median sequence number of the first AOOS code and the spread of OPO-level medians also fell over this time: in 2020, the median of the OPO-level median was 152 (interquartile range, 27-500), but by 2024 it was 33 (interquartile range, 20-73) (Fig 1A). The OPO with the lowest median first AOOS sequence number had a value of 1-2 in all study years. Results were similar when stratifying AOOS allocations by kidney donor profile index (KDPI) (Fig 1A).
Figure 1.
Changes in the use of allocation out-of-sequence (AOOS) at the level of the organ procurement organization. (A) The organ procurement organization-level median sequence number at AOOS initiation has fallen over time overall and among each strata of kidney donor profile index (KDPI). (B) Reasons for in-sequence organ offer refusal before the initiation of AOOS differ by sequence number of first AOOS code.
Reasons for in-sequence offer refusals prior to first AOOS code differed based on the sequence number of AOOS initiation (Fig 1B). In-sequence refusals for kidneys for which AOOS was initiated at sequence ≤20 were mostly recipient-related, whereas donor/organ-related in-sequence refusals predominated for kidneys for which AOOS was initiated later. Again, results were similar when stratifying AOOS allocations by KDPI (Fig S1).
Federal regulations permit allocation strategies aimed at reducing organ waste. Given the increase in allocation complexity and kidney nonuse after KAS250 was implemented, it is therefore unsurprising that AOOS also increased.6, 7, 8 However, our data demonstrate that OPOs are also initiating AOOS earlier in the allocation sequence, suggesting that they are making fewer attempts at in-sequence placement prior to turning to rescue allocation. The low median sequence number of AOOS initiation at some OPOs suggests heterogeneity in the number of in-sequence offers before initiating rescue allocation for kidneys perceived to be at risk of nonuse. Furthermore, in-sequence refusals preceding early AOOS across all strata of KDPI are rarely due to donor/organ-related concerns, supporting concerns related to AOOS subjectivity.
Limitations of this study include that organ offer refusal codes often oversimplify the complex rationale underlying each refusal, the potential for misclassification of AOOS placements, and the large number of refusals categorized as “Other.” Additionally, KDPI is an imperfect indicator of organ quality. We are unable to account for factors not captured in registry data, such as OPO-center communication outside of DonorNet and time constraints. Finally, concurrent increases in OPO aggressiveness in organ recovery may partially confound these data, as OPOs may be recovering some high-risk organs only because they have are able to use AOOS to expedite their placement with specific centers (eg, in the case of a major anatomic abnormality such as horseshoe kidneys or complex organ damage). Studying outcomes of AOOS placements is limited by an inability to determine whether any kidneys placed AOOS would have been accepted for transplant if additional in-sequence offers were made. Nevertheless, combined with evidence that AOOS is not meaningfully associated with higher utilization,9 these findings support policies aimed at replacing the current OPO-specific AOOS criteria with structured, codified, and transparent expedited allocation pathways for kidneys at high risk of nonuse. Such systems might include advanced modeling to identify kidneys at high risk of nonuse, with “ranked open offers” to multiple aggressive centers followed by placement at the center that provides the highest-ranked accepting candidate.
Article Information
Author Contributions
Research idea and study design: SAH, MEY, SM; statistical analysis: MEY; data analysis and interpretation: SAH, MEY, SM; supervision or mentorship: SM. Each author contributed important intellectual content during manuscript drafting or revision and accepts accountability for the overall work by ensuring that questions pertaining to the accuracy or integrity of any portion of the work are appropriately investigated and resolved.
Support
SAH was supported by NIDDK grant K23DK133729. SM is supported by DK116066, EB032910, DK126739, and DK130058.
Financial Disclosures
The authors declare that they have no relevant financial interests.
Acknowledgements
This study used data from the Scientific Registry of Transplant Recipients (SRTR). The SRTR data system includes data on all donors, waitlisted candidates, and transplant recipients in the United States, submitted by the members of the Organ Procurement and Transplantation Network (OPTN). The Health Resources and Services Administration (HRSA), US Department of Health and Human Services, provides oversight to the activities of the OPTN and SRTR contractors. The data reported here have been supplied by the Hennepin Healthcare Research Institute (HHRI) as the contractor for the SRTR. The interpretation and reporting of these data are the responsibility of the authors and in no way should be seen as an official policy of or interpretation by the SRTR or the US government.
Data Sharing
The data used for this analysis are available upon request to the Scientific Registry of Transplant Recipients (SRTR; srtr@srtr.org).
Peer Review
Received October 23, 2025 as a submission to the expedited consideration track with 2 external peer reviews. Direct editorial input from an Associate Editor and the Editor-in-Chief. Accepted in revised form January 05, 2026.
Footnotes
Figure S1. Reasons for in-sequence organ offer refusal before the initiation of allocation out of sequence (AOOS) by sequence number of first AOOS code, stratified by kidney donor profile index.
Table S1. Number of kidneys placed by organ procurement organizations (OPOs) following allocation out-of-sequence (AOOS) included in the analysis, by year.
Supplementary Materials
Figure S1; Table S1.
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Figure S1; Table S1.