Out of Sequence Allocation in Liver Transplantation: A Poorly Used Tool to Improve Organ Utilization.

SIGNIFICANCE

We evaluated the impact of OOS on organ utilization and also what factors impact the decision to employ OOS.

BACKGROUND

Deceased donor liver allocation typically follows a ranked match-run of potential recipients. Organ procurement organizations (OPOs) may deviate from liver transplant standardized allocation using "out-of-sequence" (OOS) matches.

METHODS

All eligible donors from the Scientific Registry of Transplant Recipients (SRTR) (1/1/2013-8/31/2023) were identified and merged with associated match-runs in the Potential Transplant Recipient (PTR) data. OOS offers were defined as bypass codes (861-863; 760-765). Hierarchical mixed-effects models with eligible donors nested in OPOs assessed OOS-practices versus organ utilization, controlling for liver graft risk with the Discard Risk Index (DSRI) by risk quintile, blood type, and year.

RESULTS

OOS were more common each progressive year. Neither TC's (R2<0.01) nor OPO's (R2<0.01) OOS-rate correlated with increased utilization. OOS was not associated with improved utilization (OR=1.11, 95%CI=0.90-1.38). Increasing graft risk in DBD&DCD grafts was associated with reduced utilization. Introducing OOS-allocation interaction terms improved utilization for DCD's of all risk levels but only improved utilization for DSRI 5th-Quintile DBD's. 38% of utilization was explained by graft factors versus 5% by TC-&OPO-variability (Conditional-R2=0.431, Marginal-R2=0.380). High-risk DCD grafts in DSRI 3rd-5th-Quintiles were not more likely to be allocated through OOS despite these grafts demonstrating improved utilization with this approach. Only 15% of variation in OOS-allocation was explained by graft factors versus 23% by TC-and OPO-variability (Conditional R2=0.388, Marginal R2=0.154).

CONCLUSIONS

OOS improves utilization in high-risk grafts, but graft risk is not correlated with their actual use. This highlights utility in OOS, but also that this practice is currently incorrectly used.