The acidity index: A simple approach to the measurement of gastric acidity

Abstract

Background: The percentage of time intragastric pH < 4 is a major parameter in evaluating the efficiency of acid-suppressive therapies. This parameter is easy to calculate, but does not identify the actual pH level. Recent studies have recommended the use of the integrated intragastric acidity as a more refined method of assessing intragastric acid control. Aim: To describe a new parameter, the acidity index, based on the logarithmic aspect of pH calculation, which may overcome the limitations of the percentage of time intragastric pH < 4 and the integrated intragastric acidity. Methods: The acidity index was calculated by obtaining the sum of 1000 x % time pH < 1, 100 x % time pH < 2 and ≥ 1, 10 x % time pH < 3 and ≥ 2 and % time pH < 4 and ≥ 3. The total percentage of time pH < 4 and the integrated intragastric acidity were calculated based on previous descriptions. The correlations between these parameters were analysed. Results: The mean ± s.d. values were 60% ± 22% for the percentage of time pH < 4, 172 ± 178 for the acidity index and 1114 ± 1176 mmol/L.h for the integrated intragastric acidity. Both the integrated intragastric acidity (r = 0.63) and acidity index (r = 0.70) showed only fair correlation with the percentage of time pH < 4. In contrast, there was a strong positive correlation (r = 0.93) between the acidity index and integrated intragastric acidity. Conclusion: The acidity index is easy to calculate, allows a more accurate assessment of the intragastric acidity than does the percentage of time pH < 4, and is comparable with the more complicated integrated gastric acidity in assessing intragastric pH control.