Should bronchodilator response be assessed in all asthmatic children with normal baseline spirometry?

Abstract

Background: Normal lung function is frequent in asthmatic children referred for lung function testing, still a positive bronchodilator response (BDR+) can be evidenced and is therefore often looked for. Objectives: To assess 1) the prevalence of BDR+ among children with normal baseline spirometry; 2) the ability of baseline spirometry indices to detect BDR+. Methods: Monocenter retrospective study between 2009 and 2017 based on the department database including all children referred for asthma. Children with normal (i.e. > -1.64 z-score) baseline forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and FEV1/FVC, along with a BDR+ (≥ 12% FEV1 increase) were compared to children with normal baseline spirometry but negative BDR (BDR-) using Z-test. The ability of FEV1 and FEV1/FVC to discriminate a BDR+ was determined after constructing Receiver Operating Characteristic (ROC) curves. Results: BDR was recorded in 7,750 files out of 8,586 (90.3%) with available baseline spirometry. Among these, 5,238 displayed a normal baseline spirometry, of which 4.9% (95% confidence interval (CI): 4.3%-5.5%) had a BDR+. ROC analysis displayed similar areas under the curve (AUC) for FEV1 (AUC=0.69, 95% CI: 0.56-0.83) and FEV1/FVC (AUC=0.71, 95% CI: 0.58-0.85). Detecting 90% of BDR+ (90% sensitivity) could be ensured by testing only cases with FEV1 z-score lower than 0.42 (68.1% total files), or with FEV1/FVC z-score lower than -0.16 (67.4% total files). Conclusions: Systematic BDR testing in asthmatic children with normal baseline spirometry reveals that only 4.9% of cases have a BDR+. Detecting 90% of BDR+ could be achieved by testing two-third of the cases.