Performance of impulse oscillometry and spirometry for the diagnosis of acute exacerbations of cystic fibrosis in adults

Background: Diagnosis of acute exacerbation (AE) of cystic fibrosis (CF) must be precise since both under- or over-prescription of antibiotics may be detrimental. How lung function tests contribute to the diagnosis of AE is unclear. Aims: We aimed to describe the diagnostic performance of spirometry and impulse oscillometry (IOS) for the diagnosis of AE. Methods: Adult CF patients were included in a retrospective single-centre study if both spirometry (FEV1, FVC) and IOS (X5, R5) data were available for at least one stable (non-AE) visit and one AE visit between December 2016 and July 2019. AE was defined by a modification of respiratory symptoms and a new antibiotic prescription. For each visit, we calculated the variation (D) in FEV1, FVC, R5 and X5 in comparison with the personal best value. Measurements were expressed as raw values, % of predicted values, and Z-scores. Areas under receiver operating characteristics curves (AUC) were computed. Results: Forty-two patients (age 28+/-9 years, FEV1 64+/-21%) were included; 104 EA visits and 80 non-EA visits were analysed. FEV1 (raw value, %pred and Z-score) and FVC (%pred and Z-score) varied significantly between AE and non-AE visits (p Conclusions: The performance of both spirometry and IOS to diagnose AE was poor. The variation in X5 (raw value) may be helpful in patients where spirometry is unreliable or uncomfortable.