Sensitivity of Lung Clearance Index and chest computed tomography in early CF lung disease

It is widely accepted that CF lung disease starts before clinical symptoms become apparent or spirometry deteriorates. Computed chest tomography (CT) is the reference method for identifying structural changes in CF; however, radiation exposure limits its use as a monitoring tool. It has been suggested that the Lung Clearance Index (LCI) measured by Multiple Breath Washout (MBW) for assessing ventilation inhomogeneity is a more sensitive surrogate marker than spirometry allowing non-invasive monitoring of CF lung disease. The aim of this study was to prospectively investigate the diagnostic accuracy of the LCI in comparison to CT in CF patients with early lung disease and normal FEV(1) (>80% pred.). MBW and ultra-low-dose CT were performed in 34 patients (6-26 years). LCI was abnormal in 76.5% subjects. LCI and CT correlated significantly in 82.3%. LCI was related to presence and extent of structural lung changes observed on CT with a sensitivity of 88%. Diagnostic accuracy of the LCI for detecting CF lung disease in patients with normal FEV(1) was good when compared to CT. Results indicate that structural changes are unlikely if a normal LCI is measured. We speculate that serial measurements of the LCI for assessing ventilation inhomogeneity may help to identify early structural lung disease and help to reduce the individual cumulative radiation dose. The LCI may be a suitable surrogate marker for monitoring progression of CF lung disease and effect of treatment in both, clinical care and research settings.