This patient's findings (macrocytic anemia with a normal serum folate level and severely depressed serum cobalamin level) suggest the presence of B12-deficiency anemia. Accompanying gastrointestinal symptoms may indicate pernicious anemia as the cause of the problem. Pernicious anemia is characterized by the autoimmune destruction of parietal cells. The two major implicated auto-antibodies that have been described are the anti-parietal and anti-intrinsic factor (IF) antibodies. Anti-IF antibody testing is the recommended initial test for the detection of pernicious anemia.
Schilling test is a classic diagnostic test of pernicious anemia that uses radio-labeled cobalamin. It is more cumbersome than antibody testing, and can be used as the second-line test if the anti-IF test is negative.
Patients with pernicious anemia are typically achlorhydric, but measurement of gastric secretions is generally not performed because it is highly invasive and non-specific.
Pernicious anemia is associated with a type of gastritis called autoimmune metaplastic atrophic gastritis (AMAG). AMAG is caused by autoimmune aggression against gastric mucosa. An immune response is mainly directed against oxyntic cells and intrinsic factor. The three main components of AMAG are glandular atrophy, intestinal metaplasia and inflammation. Atrophy affects mainly the gastric body and fundus.