Diffusing capacity of the lung for carbon monoxide: association with long-term outcomes after lung transplantation in a 20-year longitudinal study.

Rationale: The diffusing capacity of the lung for carbon monoxide corrected for haemoglobin ( ) measures gas movement across the alveolar-capillary interface. We hypothesised that is a sensitive measure of injurious allograft processes disrupting this interface.

Objectives: To determine the prognostic significance of the trajectory on chronic lung allograft dysfunction (CLAD) and survival.

Methods: A retrospective analysis was conducted of all bilateral lung transplant recipients at a single centre, between January 1998 and January 2018, with one or more measurements. Low baseline was defined as the failure to achieve a >75% predicted. Drops in were defined as >15% below recent baseline.

Results: 1259 out of 1492 lung transplant recipients were included. The median (range) time to peak was 354 (181-737) days and the mean±sd was 80.2±21.2% pred. Multivariable analysis demonstrated that low baseline was significantly associated with death (hazrd ratio (HR) 1.68, 95% CI 1.27-2.20; p<0.001). Low baseline was not independently associated with CLAD after adjustment for low baseline forced expiratory volume in 1 s or forced vital capacity. Any declines ≥15% were significantly associated with death, independent of concurrent spirometric decline. Lower percentage predicted values at CLAD onset were associated with shorter post-CLAD survival (HR 0.75 per 10%-unit change, p<0.01).

Conclusion: Low baseline and post-transplant declines in were significantly associated with survival, independent of spirometric measurements. We propose that testing may allow identification of a subphenotype of baseline and chronic allograft dysfunction not captured by spirometry. There may be benefit in routine monitoring of after lung transplantation to identify patients at risk of poor outcomes.