Achlorhydria is the most constant symptom of pernicious anemia. Indeed, the reported cases of pernicious anemia in which hydrochloric acid was present are so few that doubt has been raised as to their validity. In my experience I do not recall an instance in which achlorhydria was absent. Cases in which hydrochloric acid was present eventually proved to be diseases other than pernicious anemia. Therefore, achlorhydria may be regarded as the most decisive differential sign in establishing the diagnosis of pernicious anemia.
Following Hunter, until recently achlorhydria was regarded as secondary and consequent to gastro-intestinal sepsis of unknown origin. With more intensive study, it becomes evident that this view is untenable for the following reasons: 1. If achlorhydria were secondary, one should expect occasionally in the course of the development of anemia to witness the gradual diminution of hydrochloric acid from normal to subacidity and finally to achlorhydria. But such
MOSCHCOWITZ E. THE RELATION OF ACHLORHYDRIA TO PERNICIOUS ANEMIA. Arch Intern Med (Chic). 1931;48(2):171-186. doi:10.1001/archinte.1931.00150020002001