Impact of the lung allocation system score modification by blood type on US lung transplant candidates

The lung continuous distribution system was modified on September 27, 2023, with the goal of increasing transplant access for blood type O candidates after an error was discovered in the simulation used to support the development of the initial allocation policy. This retrospective observational study compares national waitlist outcomes (transplant rate, waitlist mortality) under continuous distribution before (March 10, 2023, through September 26, 2023; premodification) and after (September 27, 2023, through April 14, 2024; postmodification) the blood type score modification. We fit adjusted Poisson regression models of the transplant rate and mortality rate. The transplant rate was lowest for type O candidates in both eras, but significantly increased after the score modification, from a premodification adjusted rate ratio (95% CI) of 0.40 (0.36, 0.45) to postmodification 0.52 (0.45, 0.59), relative to premodification type A candidates. The adjusted mortality incidence (95% CI) decreased in type O candidates from 3.6% (3.0%, 4.3%) premodification to 3.2% (2.6%, 3.8%) postmodification. In an exploratory analysis, we estimated there would have been the same number of waitlist deaths (approximately 105) if the modified score had been adopted at the start of continuous distribution; however, transplants would have shifted toward type O candidates (57.8 [95% CI: 35.1, 80.9] additional transplants) and deaths would have shifted away from type O candidates (4.6 [95% CI: 2.7, 6.8] fewer deaths).