A 60-year-old woman with progressive fatigue has a macrocytic anemia, mean corpuscular volume 118 fL, and low serum vitamin B12. Gastric biopsy shows lymphocytic infiltration of the fundic mucosa with loss of parietal cells. Which autoantibody is the most specific marker of the condition causing her anemia?

• A Anti thyroglobulin antibody
• B Anti parietal cell antibody
• C Anti smooth muscle antibody
• D Anti intrinsic factor antibody ✓

Explanation

Autoimmune (atrophic) gastritis targets gastric parietal cells, causing loss of acid and intrinsic factor production and hence vitamin B12 malabsorption with megaloblastic anemia. Although anti parietal cell antibodies are more sensitive, they are less specific and occur in healthy elderly subjects and thyroiditis. Antibodies against intrinsic factor are highly specific for pernicious anemia and block either B12 binding or ileal uptake. Anti smooth muscle antibodies indicate autoimmune hepatitis, and anti thyroglobulin marks Hashimoto thyroiditis, which frequently coexists but does not explain the B12 deficiency.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.