title: Measurement of urea and ammonium concentrations in gastric juice.
abstract: OBJECTIVE
  To study the effect of known interference in the measurement of urea and ammonium concentrations in samples of gastric juice.
  
  
  METHODS
  The effect of pH and ammonium concentration on the o-pthalaldehyde method, the diacetylmonoxime method, a Berthelot linked method and an enzymatic urease method for the measurement of urea in gastric juice was therefore conducted. An enzymatic method of the measurement of ammonium in gastric juice was also assessed.
  
  
  RESULTS
  The o-pthalaldehyde and the enzymatic urease methods were unaffected by a low gastric juice pH, ammonium concentrations of 10 mmol/l, and had interassay coefficients of variation of 3.9-5.6% and 2.8-10.6%, respectively, over a urea concentration of 2.5 mmol/l-20 mmol/l. The Berthelot linked method resulted in low gastric juice urea concentrations. The enzymatic method of ammonium measurement also proved suitable when the effect of low gastric juice pH was controlled.
  
  
  CONCLUSIONS
  Interference by low pH did not explain the differences in reports of gastric juice urea or ammonium concentrations.
authors.affiliation: Department of Chemical Pathology, Wirral Hospital NHS Trust, Merseyside.
authors.forename: W D
authors.initials: WD
authors.lastname: Neithercut
authors.forename: A M
authors.initials: AM
authors.lastname: el Nujumi
authors.forename: K E
authors.initials: KE
authors.lastname: McColl
mesh_terms: D000641:Ammonia / Q000032:analysis*; D000643:Ammonium Chloride; D015415:Biomarkers / Q000032:analysis; D004796:Clinical Enzyme Tests; D005750:Gastric Juice / Q000737:chemistry*; D016481:Helicobacter Infections / Q000175:diagnosis; D016480:Helicobacter pylori; D006801:Humans; D006863:Hydrogen-Ion Concentration; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D014508:Urea / Q000032:analysis*; D014510:Urease / Q000032:analysis
chemical_list: D015415:Biomarkers; D000643:Ammonium Chloride; D000641:Ammonia; D014508:Urea; D014510:Urease