achlorhydria
Summary
Achlorhydria refers to the absence or marked reduction of gastric acid (HCl) secretion by parietal cells. It is classically associated with chronic atrophic gastritis (autoimmune or H. pylori-related), long-term PPI use, and gastrinoma-related compensatory states, and leads to impaired absorption of iron, B12, and calcium, along with increased susceptibility to enteric infections.
Detail
Achlorhydria results from destruction or dysfunction of gastric parietal cells, leading to loss of hydrochloric acid secretion. Causes include autoimmune metaplastic atrophic gastritis (anti-parietal cell and anti-intrinsic factor antibodies, associated with pernicious anemia and increased gastric cancer risk), chronic H. pylori infection causing atrophic gastritis, long-term proton pump inhibitor use, and rare conditions like Zollinger-Ellison syndrome post-treatment. Loss of acid secretion causes compensatory hypergastrinemia due to loss of negative feedback on G cells, which can lead to G-cell hyperplasia and increased risk of carcinoid tumors (ECL cell hyperplasia) and gastric adenocarcinoma. Clinically, achlorhydria impairs digestion and absorption: reduced acid impairs iron absorption (iron deficiency anemia), impairs vitamin B12 release from food-bound cobalamin, and in autoimmune gastritis, loss of intrinsic factor causes true B12 deficiency (megaloblastic anemia, subacute combined degeneration). Loss of the gastric acid barrier increases risk of enteric infections (e.g., Salmonella, Vibrio, Giardia) and bacterial overgrowth. Diagnosis involves gastric pH testing, elevated serum gastrin, pepsinogen I/II ratio, and endoscopic biopsy showing atrophic mucosa. Schilling test (historically) assessed B12 malabsorption. Management addresses underlying cause, B12/iron supplementation, and surveillance endoscopy for gastric cancer risk in autoimmune gastritis.
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- Goldman-Cecil Medicine
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.