It is well known that when duplicate gastric analyses are carried out the results of the two tests are often quite different. Not infrequently one test will show an absence of hydrochloric acid, while in another done at about the same time acid will be found. It has seemed worth while to try to develop some technic which would sort out the doubtful cases for further study, and so to avoid errors in diagnosis which may sometimes be of considerable importance. It seemed probable that an absence of the changes known as the "alkaline tide" in the urine might occur in cases of achlorhydria, and that urine studies might provide a method for the purpose.
The alkaline tide is a decreased acidity, or increased alkalinity, which is observed in the urine of most subjects during the day. The evidence seems to show that an increased alkalinity that develops during the
MUNFORD SA, HUBBARD RS. THE ALKALINE TIDE IN ACHLORHYDRIA. JAMA. 1926;87(12):922-924. doi:10.1001/jama.1926.02680120032010