Acid and bolus exposure in pediatric reflux disease according to the presence and severity of esophageal mucosal lesions Abstract Purpose The relationship between reflux index (RI) and bolus exposure parameters in multichannel intraluminal impedance (MII) has not been examined sufficiently among children. The significance of acid and bolus exposure in evaluating pediatric reflux disease (RD) was explored by focusing on mucosal lesions. Methods We conducted MII-pH on 28 patients (median age 8 years) with suspected RD. We assessed relationships between RI and bolus exposure indices, and also compared acid and bolus exposures across patients grouped by endoscopic esophageal mucosal lesions. Results RI correlated significantly with distal acid reflux events (r = 0.60), acid bolus exposure time (BET) (0.55), and bolus clearance time (BCT) (0.48). Significant differences were observed among the control, non-erosive RD (NERD), and erosive RD (ERD) groups in all acid and several bolus exposure indices (distal and proximal frequencies, and BCT), while no significant difference was apparent between NERD and ERD. Acid exposure tended to be more severe in high-grade than in low-grade ERD, while no similar tendency was found in any bolus parameters other than BCT. Conclusions MII-pH showed great potential for investigating the pathophysiology of pediatric RD, with RI revealing different correlations with variable bolus exposure indices. However, no specific parameters allowing precise discrimination between RDs or mucosal severities were identified.