Limitations of the dichotomized 6-minute walk distance when computing lung allocation score for cystic fibrosis: a 16-year retrospective cohort study

Purpose The 2010 Lung Allocation Score (LAS) version considers the estimated survival benefit offered by lung transplantation (LTx) and uses 6-minute Walk Test (6MWT) distance as a dichotomous covariate of whether an individual can walk more than 150 ft or 45.7 m in 6 min. This study aimed to provide evidence that 6MWT gives no clinically meaningful information to be used in the current LAS for candidates to LTx with cystic fibrosis (CF). Materials and methods We collected data from 6MWTs performed since 2003 at our CF centre. A joint model was fitted to describe the effect of changes in walked distance on the hazard of LTx or death. Results Up to 2019, 552 6MWTs were performed on 163 individuals with CF. None of the individuals included walked for less than 45.7 m during the 6MWT. Based on the joint modelling, the association of walked distance with the hazard ratio (HR) of LTx or death was significant (HR 0.99, 95% Credible Interval [CI]: 0.99 to 1.00). Conclusions When adopted dichotomously for LAS calculation, walked distance does not add any useful information about exercise capacity. Longitudinal trajectories of walked distance may provide complementary information about prognosis in individuals with CF.