title: How accurate is the determination of blood in gastric juice? Comparison of peroxidase and porphyrin methods.
abstract: BACKGROUND
  Mucosal bleeding is frequently used as a measure of gastric mucosal integrity. We compared the orthotolidine method for quantifying haemoglobin in gastric juice with a method based on measurement of fluorescent porphyrins extracted from haem. We also investigated whether acid or pepsin had a deleterious effect on the results of either method.
  
  
  METHODS
  We compared the effects of pH (2 or 7), time (up to 180 min), haemoglobin concentration and the addition of pepsin (2.5, 5 or 7.5 kU/mL hog pepsin) on the accuracy of the two methods.
  
  
  RESULTS
  With the orthotolidine method there was a time-dependent decline in detectable haemoglobin concentration (P < 0.02) at pH 2 that was not seen at pH 7. The time- and pH-dependent decline in detectable haemoglobin was not seen using the porphyrin assay.
  
  
  CONCLUSIONS
  The widely used orthotolidine method for determination of blood in gastric juice is less reliable than the porphyrin method as it is more likely to be influenced by acidic conditions in the stomach.
authors.affiliation: Department of Medicine, VA Medical Center, Houston, Texas, USA.
authors.forename: K L
authors.initials: KL
authors.lastname: Woods
authors.forename: C
authors.initials: C
authors.lastname: Kiefe
authors.forename: D Y
authors.initials: DY
authors.lastname: Graham
mesh_terms: D001560:Benzidines; D005750:Gastric Juice / Q000737:chemistry / Q000166:cytology*; D006454:Hemoglobins / Q000032:analysis; D006861:Hydrogen Peroxide; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D010434:Pepsin A / Q000032:analysis; D010544:Peroxidases / Q000032:analysis*; D011166:Porphyrins / Q000032:analysis*; D012015:Reference Standards; D012044:Regression Analysis; D015203:Reproducibility of Results
chemical_list: D001560:Benzidines; D006454:Hemoglobins; D007202:Indicators and Reagents; D011166:Porphyrins; C009501:2-tolidine; D006861:Hydrogen Peroxide; D010544:Peroxidases; D010434:Pepsin A