Objective:

To assess whether the US Candidate Risk Score (US-CRS) 2.0 identifies adult heart transplant candidates at risk of short-term mortality without transplantation more accurately than the current US 6-status allocation system.

Approach:

• Study population: Investigators analyzed Scientific Registry of Transplant Recipients data for 33,097 adult candidates listed from January 2019 through August 2025, using training, validation, and test data sets.
• Score development: They developed US-CRS 2.0 to predict 6-week mortality without transplantation, using a marginal structural model and laboratory measurements and mechanical circulatory support categories.
• Evaluation: They assessed model discrimination and calibration and simulated two allocation approaches using 45,530 historical donor-heart match runs from 2019–2024.

Key Findings:

• In the test data, the simpler US-CRS 2.0 model had a mean area under the receiver operating characteristic curve of 0.807 for 6-week mortality, compared with 0.693 for the existing 6-status system; the more complex model scored 0.795.
• Both score versions were generally well calibrated across urgency statuses, exception categories, and diagnoses, but overestimated mortality among candidates at the highest predicted risk.
• In historical match-run simulations, observed 6-week mortality among candidates ranked first was 16% under the proposed 6-status US-CRS approach and 23% under national ranking by US-CRS, compared with 11% under the existing system.
• The proposed approaches changed candidate rankings. The 6-status approach reduced donor-to-candidate distances at earlier match-run positions, while national ranking increased them.
• Both approaches prioritized more candidates from racial and ethnic minority groups at earlier match-run positions and reduced priority for candidates with blood type O and those using durable left ventricular assist devices. Changes by sex and stature were min…
• The score reflected differing mortality associations across support devices: durable left ventricular assist device use was associated with lower short-term mortality, while intra-aortic balloon pumps, microaxial flow pumps, and advanced mechanical support wer…

Interpretation:

The investigators reported that US-CRS 2.0 discriminated short-term mortality risk better than the current system in the test data and that simulated allocation approaches placed candidates with higher observed short-term mortality risk earlier in match runs. They stated that replacing the current statuses with the score could make allocation less susceptible to manipulation and save more lives.

Limitations:

• The score overestimated mortality among candidates at the highest predicted risk and may require periodic recalibration as transplant practices and heart-failure management change.
• The match-run analysis could not quantify potential effects on post-transplant survival when donor hearts are allocated to candidates with greater medical urgency.
• The proposed approaches reduced priority for candidates with blood type O and those using durable left ventricular assist devices; the investigators noted that separate allocation provisions may be needed to maintain equitable access.
• The investigators stated that a full simulation incorporating these considerations would be necessary before implementation.

Conclusion:

The study evaluated US-CRS 2.0 as a potential alternative for prioritizing adult heart transplant candidates. The authors called for further simulation before implementation.