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Intrinsic factor (IF) is synthesized in gastric parietal cells and secreted into the gastric lumen. There it complexes to vitamin B12 and then binds to receptors in the ileal mucosa, and facilitates absorption. Pernicious anemia is the commonest cause of vitamin B12 deficiency and is characterized by the severe gastric mucosal atrophy and failure to produce IF. Approximately 50% of patients with pernicious anemia have detectable antibody to IF in their plasma. A positive test for IF antibody provides strong support for the diagnosis of pernicious anemia, since false positive results are rare. However, a negative test does not rule out pernicious anemia because the sera of nearly 50% of patients with pernicious anemia do not have detectable IF antibody. Results are reported as positive, negative, and indeterminate. Specimen requirement is one SST tube of blood. This test should not be ordered if a patient has received radioisotopes or vitamin B12 within the previous week. |
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