The antiparietal cell antibody test is a blood test that detects antibodies known as anti-parietal cell antibodies (APCA) secreted against the parietal cells of the stomach. These antibodies to gastric parietal cells are associated with autoimmune gastritis and pernicious anaemia. The parietal cells are responsible for releasing a substance which is necessary for vitamin B12 absorption by the body. Parietal cell antibodies are autoantibodies produced by the immune system that falsely target the group of specialized cells that line the stomach wall. The antibodies may appear many years before the onset of pernicious anaemia. This test is used as a diagnostic test for pernicious anaemia which is one of the most common causes of vitamin B12 deficiency.