Fixed-Distance pH Probe Placement Produces Systematic Bias in Reflux Detection: The Role of Esophageal Length.

INTRODUCTION: Ambulatory esophageal pH monitoring is the reference standard for diagnosing gastroesophageal reflux disease (GERD), yet a subset of symptomatic patients demonstrate physiologically non-positive studies. OBJECTIVE: To evaluate whether variation in esophageal length and relative probe position influences measured reflux exposure and contributes to symptom-physiology discordance during wireless pH monitoring. METHODS: We performed a retrospective analysis of 63 patients undergoing Bravo pH monitoring. Relative probe position was defined as the ratio of capsule placement distance to esophageal length. Associations between anatomic variables and acid exposure time (AET) were assessed using multivariable regression, including analyses of overall, upright, and supine reflux exposure. RESULTS: Sixty-three patients were included (60% female). Height was strongly associated with esophageal length (β = 0.17, p < 0.001), resulting in systematic differences in relative probe position. A subset of patients with elevated symptom burden demonstrated physiologically non-positive reflux testing; these patients were more often female and shorter in stature. In multivariable models, taller height was independently associated with increased AET (β = 0.14, p = 0.02), an effect observed in upright reflux (β = 0.18, p = 0.030) but not supine reflux. Apparent sex differences in reflux detection were explained by underlying anatomic variation rather than sex itself. CONCLUSION: Fixed-distance pH probe placement results in variable relative positioning within the esophagus, producing non-equivalent physiologic sampling across patients. Probe placement farther from the gastroesophageal junction may under-sample clinically relevant distal reflux events and contribute to symptom-physiology discordance. Observed disparities in reflux detection among female patients appear to be driven by differences in esophageal length rather than intrinsic physiologic variation. These findings support prospective evaluation of anatomy-informed probe positioning to determine whether it can improve the consistency and diagnostic accuracy of ambulatory pH monitoring.