Lung transplant is a life-saving intervention for many with end-stage lung disease. As usable donor lungs are a limited resource and the risk of death on the waitlist is not uniform among candidates, organ allocation must consider many variables in order to be equitable.

The lung allocation score (LAS) system, implemented in 2005, accounted for disease severity, risk of death without transplant, and 1-year survival estimates; however, recipient size, allosensitization, and blood type, biologic features that influence donor pool for a given recipient, do not impact allocation priority. Additionally, social determinants such as geography, socioeconomic status, race, and ethnicity can impact the likelihood of receiving a transplant. This has resulted in certain groups being transplanted at lower rates and at higher risk of dying on the waitlist. In order to address these disparities, lung organ allocation in the United States transitioned to a continuous distribution system using the composite allocation score (CAS) on 9 March 2023.

In this article, we will review some of the data demonstrating the impact that biologic and social determinants have had on lung allocation in order to provide background as to why these have been incorporated into the CAS.