Mean acidity or percentage reflux time in oesophageal pH-monitoring

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Abstract
Objectives: The reflux parameter mean acidity, which is independent of any pH threshold, was compared with the established parameter percentage of time when the pH is less than 4 with respect to the discriminatory diagnostic accuracy in gastro-oesophageal reflux disease and the evaluation of drug effects. Methods: Normal values, sensitivity and specificity of pH-monitoring were calculated using receiver operating characteristic (ROC) analysis in 35 reflux patients and 19 healthy controls. In addition, 32 patients were studied twice, without medication (baseline) and with either antacids (five patients), ranitidine (13 patients) or omeprazole (14 patients). Results: The percentage reflux time was superior to the mean acidity in the diagnosis of gastro-oesophageal reflux disease (maximal sensitivity/specificity was 91/95% compared with 83, 84%). Antacids did not reduce the percentage reflux time or the mean acidity. Ranitidine only reduced the percentage reflux time for the supine body position from 7.7 (0.2–46.4) to 0.72% (0.0–14.9, P < 0.05). Omeprazole reduced all reflux parameters; the percentage reflux time for the upright body position from 9.6 (5.0–52.3) to 1.6% (0.0–22.5, P < 0.01) and for the supine position from 4.9 (0.0–23.7) to 0.0% (0.0–48.5, P < 0.050, and the mean acidity from 0.84 (0.02–76.0) to 0.01 mmol/l (0.0–0.71, P < 0.001). Mean acidity described the effect of omeprazole significantly better than percentage reflux time. Conclusions: In the diagnosis of gastro-oesophageal reflux disease, percentage reflux time is superior to mean acidity. Mean acidity, however, seems to be the better parameter to describe the reduction in acid gastro-oesophageal reflux afforded by potent antisecretory drugs.

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