A supply-based scoring approach to account for biological disadvantages in accessing lung transplant

The lung Composite Allocation Score (CAS) accounts separately for biological disadvantages stemming from candidate blood type and height using consensus-derived heuristics, which do not reflect the true supply of compatible organs available to candidates with specific combinations of blood type and height. Here, we develop an alternative CAS biological disadvantages subscore using a novel measure of donor supply.

Using Scientific Registry of Transplant Recipients data from February 19, 2015 to September 1, 2021, we modeled daily distance-adjusted supply of compatible donors, as a function of candidate blood type, height, and diagnosis group, using Poisson rate regression and applied the model to create a 10-point supply-based subscore. Substituting this subscore in place of the 10 total points allocated to blood type and height in CAS created a "Supply-Adjusted CAS". We simulated population outcomes under Supply-Adjusted CAS, original CAS (March 2023) and "ABO Modified" CAS (September 2023).

The supply-based subscore was more responsive to variations in candidate blood type, height, and diagnosis group than corresponding CAS or ABO-Modified CAS subscores. In simulation, waitlist mortality improved from 13.95 per 100 waitlist years under CAS and 14.12 under ABO-Modified CAS to 13.09 under Supply-Adjusted CAS. Transplant rates improved from 121.6 and 126.2 under CAS and ABO-Modified CAS, respectively, to 128.8 under Supply-Adjusted CAS. Height disparities improved substantially, while blood type disparities grew slightly relative to ABO-Modified CAS.

Supply-Adjusted CAS may improve lung transplant population outcomes overall while providing a more empirically based method to address equity.