Agreement between spirometry and impulse oscillometry for lung function assessment in 6‐year‐old children born extremely preterm and at term

BACKGROUND: Extremely preterm birth is a risk factor for reduced lung function later in life, and clinical follow‐up from early childhood is recommended. Dynamic spirometry is the most widely used method to assess airway obstruction, but impulse oscillometry (IOS) may be an alternative method that is easier to perform in young children. The feasibility and agreement between spirometry and IOS outcome variables has not been investigated in children born extremely preterm. AIM: To determine the feasibility of and correlation between spirometry and IOS in pre‐school children born extremely preterm. METHODS: Spirometry and IOS were performed in 6‐year‐old children born extremely preterm (n = 88) and age‐matched term controls (n = 84) in Stockholm, Sweden. Correlations between spirometry and IOS outcome variables were analyzed using Pearson's partial correlation, adjusting for height. RESULTS: Success rate for spirometry (60%) was lower than for IOS (93%) but did not differ significantly between the preterm and term groups (56% and 64% for spirometry, P = .25; and 92% and 94% for IOS, P = .61). Correlations between spirometry and IOS outcomes were at best moderate (Spearman's r = −0.31 to −0.56). Normal IOS identified 69% to 90% of those with normal spirometry. A negative predictive value of 90% was found for R5‐R20 versus FEV(0.75)/FVC, suggesting that IOS may be used to exclude obstructive airway disease as measured by spirometry. CONCLUSION: IOS is a more feasible method than spirometry to assess lung function in young children irrespective of gestational age at birth and could be considered an alternative in children who cannot perform spirometry.