Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (716 page)

   Antibodies to gastric parietal cells that react with the cell membrane, cytoplasmic antigens, or gastric intrinsic factor are present in essentially all (>90%) of individuals with pernicious anemia. In 70% of patients, antibodies reactive with the vitamin B
₁₂
–binding site of intrinsic factor are present, and in 50% of patients, additional antibodies are present, which react with a second antigenic site on the 44,000-Da intrinsic factor protein molecule. These autoantibodies lead to a pathologic immune process termed “chronic autoimmune gastritis,” which may slowly progress for 10–20 years and finally terminate in gastric atrophy. The gastric atrophy results in a lack of absorption of vitamin B
₁₂
and leads to megaloblastic anemia in patients with anti–parietal cell antibodies. Pernicious anemia is associated with a variety of other autoimmune diseases including thyrotoxicosis, Hashimoto thyroiditis, insulin-dependent DM, primary Addison disease of the adrenals, primary ovarian failure, primary hypoparathyroidism, vitiligo, Myasthenia gravis, and the Lambert-Eaton syndrome.

   
Normal range:

   IFA: negative; if positive, results are tittered, ELISA: <1:40 titer.

   APC titers greater than 1:40 are significant.

   Use

   Aids in the evaluation of patients suspected of having pernicious anemia

   Evaluation of immune-mediated deficiency of vitamin B
₁₂
with or without megaloblastic anemia

   Interpretation

Increased In

   Pernicious anemia

   Atrophic gastritis

   Diabetes

   Gastric ulcer

   Thyroid disease