title: Gastric-juice ammonia assay for diagnosis of Helicobacter pylori infection and the relationship of ammonia concentration to gastritis severity.
abstract: OBJECTIVE
  To determine the test characteristics of gastric-juice ammonia concentration as measured by an ion-selective electrode and a rapid ammonia detection device for the diagnosis of Helicobacter pylori infection and to assess the relationship between gastric-juice ammonia concentration and the severity of gastritis.
  
  
  METHODS
  Patients undergoing upper endoscopy had collection of gastric juice that was tested for ammonia using an ion-selective electrode and a rapid ammonia assay device that uses a pH-indicating membrane. A receiver operating characteristic curve was calculated for ammonia concentration. Severity of gastritis was graded using the Sydney classification (1) and correlated to gastric-juice ammonia concentration. Patients also underwent H. pylori testing by IgG serology, rapid urease testing, and histological special stain. Ammonia testing results were compared with a reference standard of two of three positive tests and with a second reference standard of a positive serology.
  
  
  RESULTS
  73 patients underwent endoscopy and collection of gastric juice. The receiver operating characteristic curve indicated an optimal cutoff value of 5 mM, yielding a sensitivity of 67%, specificity of 93%, positive predictive value of 67%, and negative predictive value of 93% (compared with the combined reference standard). The rapid NH3-testing device yielded a sensitivity of 83%, specificity 63%, positive predictive value 31%, and negative predictive value 95%. The severity of neutrophilic (p = 0.001) and mononuclear cell (p = 0.003) infiltration were significantly correlated with gastric-juice ammonia concentration.
  
  
  CONCLUSIONS
  Measurement of gastric-juice ammonia concentration by ion-selective electrode or rapid detection device is a relatively insensitive and nonspecific means of H. pylori diagnosis. Gastritis severity increases with gastric-juice ammonia concentration.
authors.affiliation: Department of Medicine, Seattle Veterans Administration Medical Center, Washington 98108, USA
authors.forename: D J
authors.initials: DJ
authors.lastname: Kearney
authors.forename: K
authors.initials: K
authors.lastname: Ritchie
authors.forename: J S
authors.initials: JS
authors.lastname: Peacock
mesh_terms: D000641:Ammonia / Q000032:analysis*; D005260:Female; D005750:Gastric Juice / Q000737:chemistry*; D005756:Gastritis / Q000175:diagnosis / Q000382:microbiology*; D005773:Gastroscopy; D016481:Helicobacter Infections / Q000175:diagnosis* / Q000453:epidemiology; D016480:Helicobacter pylori; D006801:Humans; D017736:Ion-Selective Electrodes; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012372:ROC Curve; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
chemical_list: D000641:Ammonia