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

Abstract

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 center dot 0 to 6 center dot 4 in the upright position and from 4 center dot 5 to 5 center dot 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 gastrooesophageal reflux, but are reluctant to advocate the use of higher thresholds in clinical practice.

Gastro-oesophageal reflux monitoring: review and consensus report on detection and definitions of acid, non-acid, and gas reflux

“…It was also suggested that the specificity of pH measurement could be improved if the pH recovery level was increased to 5 instead of 4, as many non-reflux related fluctuations in pH occur at around pH 4. 44 The use of combined pH monitoring and impedance measurement would permit detection of acid reflux episodes and would also obviate the need to use duration criteria, as the impedance criteria define whether or not reflux has occurred. The occurrence of reflux episodes when the basal oesophageal pH is already below 4 was discussed in some detail.…”

Intra-oesophageal pH profiles and pharmacokinetics of pantoprazole and esomeprazole

“…Indeed, a pH of , 4.0 has proved to be the most acceptable threshold in clinical practice, although others have been defined [23]. Nevertheless, in order to compare our results with the maximum number of results from other studies, we calculated pH-metry parameters for the thresholds pH Median intra-oesophageal pH-profiles (n ¼ 35, first/third quartile) at baseline (a) and at day 7 after repeated administration of pantoprazole 40 mg once daily at 08.00 (b).…”

Reflux monitoring: pH-metry, Bilitec and Oesophageal impedance measurements

“…This cutoff value has been challenged over the years by studies suggesting that a pH value of 5 may provide better discrimination between healthy volunteers and patients with reflux symptoms [15]. Other authors have suggested that the best discrimination between patients with reflux symptoms and healthy volunteers occurs within the full range between pH 3 and 6 rather than using one single pH value [16] or by studies proposing different pH threshold values for different positions based on pH distribution curves [17]. However the simplicity of using a single cutoff value prevailed and pH 4.0 is currently the most widely used cutoff value to identify gastro-oesophageal reflux episodes in ambulatory oesophageal pH monitoring.…”