Chronic atrophic gastritis has no specific clinical manifestations, so the diagnosis of chronic atrophic gastritis requires clinical manifestations combined with relevant ancillary examinations, especially gastroscopy and gastric mucosal biopsy. The following systematically introduces the diagnostic basis of chronic atrophic gastritis: 1. Clinical manifestations Mainly loss of appetite, nausea, belching, epigastric fullness or dull pain, a few patients can have upper gastrointestinal bleeding, emaciation, anemia, brittle nails, tongue inflammation or tongue papillae atrophy, etc. 2, laboratory tests (1) gastric fluid analysis: patients with type A CAG mostly have no acid or low acid, while patients with type B CAG may have normal or low acid. (2) Pepsinogen determination: pepsinogen is secreted by the main cells. In chronic atrophic gastritis, the content of pepsinogen in blood and urine is reduced. (3) Serum gastrin measurement: G cells in the mucosa of the gastric sinus secrete gastrin; in patients with type A CAG, serum gastrin is often significantly increased; in patients with type B CAG, atrophy of the gastric sinus mucosa directly affects the gastrin-secreting function of G cells, and serum gastrin is lower than normal. (4) Immunological examination: Antibodies to mural cells, antibodies to endogenous factors, and antibodies to gastrin-secreting cells can be used as an auxiliary diagnosis of chronic atrophic gastritis and its subtypes. 3.X-ray examination X-ray gastric barium meal examination is not abnormal in most patients with atrophic gastritis. The gas-barium double imaging can show the flattening and thinning of the mucosal folds of the gastric body, the thinning or disappearance of the serrated mucosal folds of the large curve of the gastric body, the smoothness of the gastric bottom, and the serrated or coarse mucosal disorder of the gastric mucosa in some cases of gastric sinusitis. 4, gastroscopy and biopsy Gastroscopy and biopsy are the most reliable diagnostic methods. Gastroscopic diagnosis should include the location of the lesion, the degree of atrophy, intestinal metaplasia and atypical hyperplasia. The mucosa of atrophic gastritis is mostly pale or grayish with thinning or flattening of the folds when observed by direct visualization with the naked eye. The mucosa may show red and white, with scattered white patches in severe cases. Submucosal vascularity is characteristic of atrophic gastritis, and small red reticular arteries or capillaries may be seen. In severe atrophic gastritis, epithelial cell hyperplasia is seen forming small granules or larger nodules. There is also mucosal erosion and bleeding. Gastric mucosal biopsy pathology is mainly characterized by varying degrees of glandular atrophy and loss, replaced by pyloric glandular hyperplasia or intestinal glandular hyperplasia, with significant interstitial inflammatory infiltration.