Anti-parietal cell antibodies (APCA) are autoantibodies directed against the H+/K+-ATPase proton pump on gastric parietal cells. Parietal cells are responsible for producing both hydrochloric acid and intrinsic factor, a protein essential for vitamin B12 absorption in the small intestine. When the immune system attacks these cells, it causes autoimmune atrophic gastritis.
Progressive parietal cell destruction reduces stomach acid production and, critically, reduces intrinsic factor output. Without intrinsic factor, vitamin B12 cannot be absorbed from food, eventually causing pernicious anaemia and B12 deficiency with neurological consequences. APCA are found in up to 90% of people with pernicious anaemia but are also present in a significant proportion of older adults and people with other autoimmune conditions without pernicious anaemia.
FAQs
What is pernicious anaemia?
Pernicious anaemia is a type of megaloblastic anaemia caused by autoimmune destruction of gastric parietal cells, leading to loss of intrinsic factor and inability to absorb vitamin B12 from food. It causes B12 deficiency with neurological complications and megaloblastic (large red cell) anaemia. Treatment is with lifelong B12 injections.
Is APCA the same as testing for pernicious anaemia?
APCA is associated with pernicious anaemia but is not sufficient alone for diagnosis. Intrinsic factor antibody (IFA) testing is more specific for pernicious anaemia. Diagnosis requires combining antibody results with B12 levels, clinical features, and sometimes gastroscopy with biopsy.
Can I have APCA without pernicious anaemia?
Yes. APCA is present in many people, particularly older adults, without developing clinical pernicious anaemia. However, APCA-positive individuals have an increased risk of developing B12 deficiency over time and should be monitored regularly.
Is there a link between autoimmune thyroid disease and APCA?
Yes. Approximately 30-40% of people with Hashimoto's thyroiditis have APCA, reflecting the tendency of autoimmune conditions to cluster together in genetically predisposed individuals. People with autoimmune thyroid disease should have B12 levels monitored periodically.
