Lung function testing in children with airway disease: Does their performance deviate from healthy LUNOKID children?

In the LUNOKID study (lung function normal values for kids in Germany) lung function was measured in 4- to 18-year-old subjects (n=5104). Spirometric reference values were developed after exclusion of children with airway disease. In the present data analysis, we investigate differences between children with airway disease and healthy children, with respect to 1) fulfilment of ATS/ERS quality criteria, and 2) results regarding lung function values. In the study population, there were 417 children with asthma (195 without current medication), 734 with upper respiratory tract infection on the day of investigation (URTI), 180 with lower respiratory tract infection (LTRI) within 6 weeks prior to testing, 629 with a history of wheezy bronchitis (WB), and 3133 subjects were healthy with respect to airway disease. A total of 3205 children fulfilled ATS/ERS quality criteria. Compared to healthy children, less children with URTI delivered visually acceptable manoeuvres (72% and 62%, resp., p<0.01), whereas asthmatics performed better (80%, p<0.01). No other statistically significant differences were observed. Upon analysis of FEV1, FVC, FEV1/FVC in the acceptable manoeuvres, only asthma was associated with a physiologically relevant lower lung function (mean LUNOKID based z-score < -0.50) compared to healthy children: Mean z-score for FEV1/FVC was -0.53 with asthma medication, -0.67 without. In the other disease groups, there were no relevant differences from the healthy LUNOKID population. We suggest that neither current URTI nor LRTI within 6 weeks nor a history of WB are reasons to exclude subjects from analysis when developing reference values for FEV1, FVC, and FEV1/FVC.