# Expedited Transplant Allocation Using a Paired Kidney Cohort

## TL;DR

This study examines how often one kidney from a donor is transplanted out of sequence while the other is transplanted in sequence, and finds no significant difference in outcomes between the two.

## Contribution

The study identifies a 17-fold increase in unilateral out-of-sequence kidney allocation and provides insights into the factors influencing this allocation strategy.

## Key findings

- Unilateral out-of-sequence allocation increased 17-fold from 2020 to 2024.
- There were no significant differences in patient or graft survival between in-sequence and out-of-sequence transplants.
- Out-of-sequence allocation decisions were not clearly linked to organ quality or timing.

## Abstract

This cohort study estimates the incidence of unilateral out-of-sequence transplants, in which 1 kidney is placed in sequence and the other kidney from the same donor is placed out of sequence.

How frequently does out-of-sequence allocation of a kidney follow in-sequence placement of a kidney from the same donor, and what are the survival outcomes of recipients?

In this cohort study of 15 602 kidneys from 8544 deceased donors, unilateral out-of-sequence allocation increased 17-fold, with the first attempt occurring at a median sequence number of 28 in 2024 (vs 393 in 2020). There were no significant differences in patient or graft outcomes between unilateral out-of-sequence and unilateral in-sequence transplants.

Restricting analyses to cases in which the allocation system was successful for the contralateral kidney raises questions about how organ procurement organizations decide to perform out-of-sequence allocation, given that neither organ quality nor timing appeared to be associated with this decision.

Organ procurement organizations are increasingly turning to expedited (ie, out-of-sequence) allocation of deceased donor kidneys, citing maximal utility of kidneys at risk of nonuse.

To identify and compare kidney pairs from the same donor from whom 1 kidney was transplanted in sequence and the other out of sequence.

This retrospective cohort study used US kidney transplant registry data obtained from the Scientific Registry of Transplant Recipients to identify kidney transplant donors from whom at least 1 deceased donor kidney was transplanted out of sequence in 2020 through 2024.

Incidence of unilateral out-of-sequence transplants, in which 1 kidney was placed in sequence and the other kidney from the same donor was placed out of sequence, and survival outcomes of recipients.

A total of 15 602 kidneys from 8544 deceased donors (5304 [62.1%] male; mean [SD] age at organ recovery, 44.4 [15.1] years) with at least 1 kidney transplanted out of sequence were included in the analysis. Of these, 4313 donors (50.5%) had a unilateral kidney placed out of sequence. Compared with recipients of unilateral in-sequence kidneys, recipients of unilateral out-of-sequence kidneys included a greater percentage of older (median [IQR] age at transplant, 60.0 [50.0-67.0] vs 57.0 [47.0-65.0] years), Asian (472 [10.9%] vs 282 [6.5%]), White (2391 [66.1%] vs 2197 [50.9%]), and male (2850 [66.1%] vs 2453 [56.9%]) recipients, as well as those with private insurance (1255 [29.1%] vs 990 [23.0%]) and preemptive transplant (739 [17.1%] vs 438 [10.2%]) (all P < .001). Unilateral out-of-sequence kidneys accounted for 38.2% of all out-of-sequence transplants over the course of the study period. From 2020 through 2024, unilateral out-of-sequence kidneys increased from 97 instances from 15 organ procurement organizations to 1698 kidneys from all 56 organizations in the US. The first instance of an out-of-sequence refusal code (ie, the point in the waiting list at which kidneys were first placed out of the standard sequence) decreased from median (IQR) sequence number 393 (155-889) in 2020 to 28 (11-77) in 2024. The proportion of donor-related reasons for refusal decreased 10% to 15% during the study period. In adjusted Cox models, outcomes for unilateral out-of-sequence transplant were not significantly different for patient survival (hazard ratio, 0.84 [95% CI, 0.70-1.02]; P = .08) or graft survival (hazard ratio, 0.87 [95% CI, 0.70-1.08]; P = .20), compared with unilateral in-sequence transplant.

Findings from this cohort study of unilateral out-of-sequence transplants highlight the importance of understanding donor and allocation factors that resulted in bypassing standard allocation and are critical to designing future iterations of the organ allocation system with improved organ use rates.