​Diagnosis of pernicious anaemia (positive in ~70% of patients with pernicious anaemia).

Pernicious anaemia is a chronic disease at the end stage of type A (autoimmune) chronic atrophic gastritis. Type A is autoimmune in nature and associated with pernicious anaemia. Type B (non-autoimmune) is associated with H.pylori infection. During the progression of type A chronic atrophic gastritis, gastric parietal cells which produce intrinsic factor and HCl, and zymogenic cells which produce pepsinogen, are destroyed and production of Intrinsic Factor (IF) and HCl is eliminated. Intrinsic Factor is essential for the absorption of vitamin B₁₂ from the intestine and its absence leads to vitamin B₁₂ deficiency and megaloblastic anaemia. Diagnosis of pernicious anaemia is important for the treatment of the anaemia itself and prevention of irreversible neurological damage. Circulating antibodies to Intrinsic Factor are highly specific and can be detected in >50% of cases with pernicious anaemia. These antibodies are of 2 types: Type 1, blocking antibodies which prevent the binding of vitamin B₁₂ to the IF molecule and Type 2 antibodies which may interfere with the binding of the IF-vitamin B₁₂ complex to the ileal receptor.