Measurement of gastric pH in ambulatory esophageal pH monitoring

Ambulatory esophageal pH monitoring is the method used most widely to quantify gastroesophageal reflux. The degree of gastroesophageal reflux may potentially be underestimated if the resting gastric pH is high. Normal subjects and symptomatic patients undergoing 24-h pH monitoring were studied to determine whether a relationship exists between resting gastric pH and the degree of esophageal acid exposure. Normal volunteers (n = 54) and symptomatic patients without prior gastric surgery and off medication (n = 1,582) were studied. Gastric pH was measured by advancing the pH catheter into the stomach before positioning the electrode in the esophagus. The normal range of gastric pH was defined from the normal subjects, and the patients then were classified as having either normal gastric pH or hypochlorhydria. Esophageal acid exposure was compared between the two groups. The normal range for gastric pH was 0.3-2.9. The median age of the 1,582 patients was 51 years, and their median gastric pH was 1.7. Abnormal esophageal acid exposure was found in 797 patients (50.3%). Hypochlorhydria (resting gastric pH > 2.9) was detected in 176 patients (11%). There was an inverse relationship between gastric pH and esophageal acid exposure (r = -0.13). For the patients with positive 24-h pH test results, the major effect of gastric pH was that the hypochlorhydric patients tended to have more reflux in the supine position than those with normal gastric pH. There is an inverse, dose-dependent relationship between gastric pH and esophageal acid exposure. Negative 24-h esophageal pH test results for a patient with hypochlorhydria may prompt a search for nonacid reflux as the explanation for the patient's symptoms.