title: Improving the analysis of esophageal acid exposure by a new parameter: area under H+.
abstract: OBJECTIVE
  We aimed to compare the data provided by 24-h continuous esophageal pH monitoring in a group of patients with gastroesophageal reflux disease (GERD) to those from a group of healthy volunteers using both conventional parameters and calculated area under the curve of hydrogen ion activity (AUH+), a new value that describes the true acid exposure, through both duration and depth of acidity changes.
  
  
  METHODS
  Thirty healthy controls and 60 patients with GERD (30 symptomatic patients without endoscopic esophagitis or nonerosive GERD and 30 symptomatic patients with Savary I-IV endoscopic esophagitis or erosive GERD) were enrolled in a study based on 24-h pH monitoring to compare reference values by means of receiver operating characteristic (ROC) discriminant analysis.
  
  
  RESULTS
  The best ROC cutoff value for nonerosive GERD patients was AUH+ = 103.7 (mmol/L) x min with sensitivity of 76.7% and specificity of 93.3%. The best ROC cutoff value for erosive GERD patients was AUH+ = 114.1 (mmol/L) x min with sensitivity of 100% and specificity of 96.7%. These cutoff values increase the sensitivity by 16.7% for nonerosive GERD patients and 10% for erosive GERD patients when compared to a common parameter such as the percentage of total time pH is <4 with a limit of 4.2%.
  
  
  CONCLUSIONS
  AUH+ is a valid quantitative parameter to measure 24-h esophageal acid exposure. It may be a reliable and significant clinical aid because it is a more sensitive test in discriminating negative or positive adult patients with or without esophagitis who are submitted to 24-h esophageal pH monitoring.
authors.affiliation: Department of Surgery, University of Turin, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Rebecchi
authors.forename: Francia Italo
authors.initials: FI
authors.lastname: Di
authors.forename: Claudio
authors.initials: C
authors.lastname: Giaccone
authors.forename: Mario
authors.initials: M
authors.lastname: Morino
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004947:Esophagus / Q000378:metabolism* / Q000503:physiopathology*; D005260:Female; D005764:Gastroesophageal Reflux / Q000175:diagnosis* / Q000503:physiopathology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000379:methods*; D011522:Protons; D012372:ROC Curve; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D011522:Protons