Objective determination of pH thresholds in the analysis of 24 h ambulatory oesophageal pH monitoring

In 24 h oesophageal pH monitoring, pH 4 is widely but arbitrarily used as the threshold between reflux and non-reflux pH values. The aim of the study was to define pH thresholds objectively, based on Gaussian curve fitting of pH frequency distributions. Single-channel 24 h oesophageal pH monitoring was performed in 26 healthy volunteers and 26 patients with pathological gastro-oesophageal reflux, and five-channel pH;metry was performed in 14 healthy volunteers and 14 patients. The calculated pH thresholds varied between healthy volunteers from 5.0 to 6.4 in the upright position and from 4.5 to 5.7 in the supine position, but were constant between different oesophageal recording sites. In 15 and nine patients (single-channel and five-channel pH-metry respectively), pH thresholds could not be determined at the distal oesophageal sites. However, the calculated pH thresholds in the proximal oesophagus were in the same range as in the control subjects. The authors conclude that the use of the conventional threshold of pH 4 leads to underestimation of the extent of gastro-oesophageal reflux, but are reluctant to advocate the use of higher thresholds in clinical practice.