What are the diagnostic steps for autoimmune gastritis?

Diagnostic Approach to Autoimmune Gastritis

The definitive diagnosis of autoimmune gastritis requires a combination of serological testing for specific antibodies and histological confirmation through endoscopic biopsies of the gastric corpus and antrum. 1

Initial Diagnostic Evaluation

• Suspect autoimmune gastritis in patients with unexplained iron deficiency anemia (especially if resistant to oral replacement therapy) or vitamin B12 deficiency 2, 3
• Consider autoimmune gastritis in patients with other autoimmune disorders, particularly autoimmune thyroid disease 1, 4
• Initial laboratory evaluation should include:
  • Complete blood count to assess for anemia 3
  • Iron studies (serum iron, ferritin, total iron binding capacity) 1, 4
  • Vitamin B12 levels 1, 3
  • Serum gastrin levels (typically elevated in autoimmune gastritis) 2, 4

Serological Testing

• Anti-parietal cell antibodies (PCA) - present in 80-90% of patients with autoimmune gastritis 2, 3
• Anti-intrinsic factor antibodies (IFA) - highly specific but less sensitive (present in approximately 30-50% of cases) 2, 5
• Combined testing of both antibodies improves diagnostic accuracy 2
• Consider testing for H. pylori antibodies to help differentiate between H. pylori-associated atrophic gastritis and autoimmune gastritis 1, 2

Endoscopic Evaluation

• Upper endoscopy with targeted biopsies is essential for definitive diagnosis 1
• Endoscopic features of autoimmune gastritis include:
  • Pale appearance of gastric mucosa 1
  • Increased visibility of submucosal vasculature due to mucosal thinning 1
  • Loss of gastric folds, particularly in the corpus and fundus 1
  • Possible presence of light blue crests and white opaque fields if intestinal metaplasia is present 1

Biopsy Protocol

• Obtain biopsies from both the gastric corpus and antrum/incisura and place in separately labeled containers 1
• Targeted biopsies should be taken from any visible abnormalities 1
• Histological features suggestive of autoimmune gastritis include:
  • Corpus-predominant atrophic gastritis 1
  • Loss of parietal and chief cells 1
  • Pseudopyloric and intestinal metaplasia 1
  • Chronic inflammatory infiltrate 1, 3
  • Possible enterochromaffin-like (ECL) cell hyperplasia 1, 4

Diagnostic Pitfalls and Considerations

• The AGA suggests against routine gastric biopsies to diagnose autoimmune atrophic gastritis in patients with iron deficiency anemia alone, recommending a more targeted approach 1
• Autoimmune gastritis is often asymptomatic until advanced stages, leading to delayed diagnosis 6, 7
• Differential diagnosis must include H. pylori-associated atrophic gastritis, which typically involves the antrum and can extend to the corpus, while autoimmune gastritis is restricted to the corpus 1
• False negative results can occur if patients have already been treated with vitamin B12, which may reduce antibody titers 4, 5
• Consider the "serological biopsy" approach (combined testing of PCA, IFA, gastrin levels, and H. pylori antibodies) as an initial screening tool before proceeding to endoscopy 2

Follow-up Evaluation

• Patients diagnosed with autoimmune gastritis should be evaluated for:
  • Concomitant autoimmune disorders, particularly autoimmune thyroid disease 1
  • Gastric neuroendocrine tumors (type 1) 1
  • Gastric adenocarcinoma risk 3, 4
• Consider surveillance endoscopy every 3 years in patients with advanced autoimmune gastritis 1
• Monitor iron and vitamin B12 levels regularly to guide replacement therapy 1, 4