Reproducibility of proximal probe pH parameters in 24-hour ambulatory esophageal pH monitoring.

OBJECTIVES: To assess the reproducibility and reliability of the proximal pH probe in detecting acid reflux into the proximal esophagus.
METHODS: Using dual probe ambulatory esophageal pH monitoring, we studied 32 subjects (11 healthy control subjects, 10 patients with distal esophageal acid reflux, and 11 patients with both distal and proximal esophageal acid exposure) on two separate days within a 20-day period. The distal pH probe was placed 5 cm above the manometrically determined lower esophageal sphincter, and the proximal probe was positioned immediately distal to the upper esophageal sphincter. Patients were categorized on the basis of the esophageal pH data obtained during the first study. Reflux parameters assessed were the percentages of time in which pH was <4 in the total, upright, and supine positions. To be considered reproducible, all three of the above parameters had to remain in the same category as the first day's results.
RESULTS: Intrasubject reproducibility of the proximal probe was 91-100% in healthy subjects, 70-90% in patients with distal esophageal acid reflux, and 45-73% in patients with proximal esophageal acid reflux. The proximal probe reproducibility for the overall diagnosis of gastroesophageal reflux disease was 91% in healthy subjects, 70% in patients with distal esophageal acid reflux, and only 55% in those with proximal esophageal acid reflux. Statistical analysis demonstrated only a fair index of concordance (kappa = 0.40) for the proximal probe.
CONCLUSIONS: The proximal pH probe has excellent specificity (91%) but poorer sensitivity and reproducibility (55%) for identifying abnormal amounts of proximal esophageal acid reflux. Therefore, a negative test result does not exclude proximal reflux with microaspiration as a cause of atypical reflux symptoms.