Determination of antibodies against intrinsic factor is used for laboratory diagnosis and documentation of pernicious anemia.
The intrinsic factor is a glycoprotein that is produced by the gastric parietal cells and is essential for the absorption of vitamin B12 from the diet. During digestion, gastric acids separate vitamin B12 from food and the intrinsic factor binds to vitamin B12 and allows it to be absorbed into the small intestine. Various conditions affecting intrinsic factor production lead to malabsorption and deficiency of vitamin B12. Laboratory findings of B12 deficiency include decreased serum B12 levels, increased methylmalonic acid, and megaloblastic anemia. The reduced hemoglobin synthesis associated with B12 deficiency is characterized by abnormal maturation of precursor erythrocytes in the bone marrow, which results in the presence of megaloblasts, the presence of hypersegmented neutrophils, and reduced erythrocyte survival. Vitamin B12 deficiency is also associated with neurological disorders.
Unfortunately, many other pathological conditions that require different interventions can mimic the symptoms and signs of vitamin B12 deficiency. However, even when vitamin B12 deficiency has been established, clinical improvement may require different dosages or routes of administration of vitamin B12, depending on the underlying cause. Patients with pernicious anemia, which is probably the most common type of B12 deficiency in developed countries, require either large doses of oral vitamin B12 or parenteral replacement therapy. The reason is that patients with pernicious anemia suffer from gastric mucosal atrophy, which is probably caused by a catastrophic autoimmune process. This results in reduced production of gastric acid, pepsin, and intrinsic factor. Gastric acid and pepsin are required for the release of vitamin B12 from food proteins, while the intrinsic factor binds free vitamin B12, transports it to receptors in the intestinal mucosa, and facilitates its absorption.
Most patients with pernicious anemia have autoantibodies against the gastric parietal cells or to the intrinsic factor. Antibodies against the intrinsic factor are very specific for the diagnosis of pernicious anemia but are found in only 50% of cases. In contrast, antibodies against parietal cells are found in approximately 90% of patients with pernicious anemia but are also found in a significant proportion of patients with other autoimmune diseases, as well as in approximately 2-10% of healthy individuals (this rate increases with age).
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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