Which condition results from a deficiency of intrinsic factor leading to abnormal red blood cell production when vitamin B12 is deficient?

• A. Rheumatoid arthritis
• B. Hay fever
• C. Autoimmune hemolytic anemia
• D. Pernicious anemia

Answer: (D)

Intrinsic factor is a stomach-produced substance essential for absorbing vitamin B12 in the small intestine. When intrinsic factor is deficient, vitamin B12 isn’t absorbed properly, leading to a deficiency that impairs DNA synthesis in red blood cell precursors. This causes megaloblastic, macrocytic anemia—characteristic of pernicious anemia—which occurs when the body cannot absorb enough B12 due to lack of intrinsic factor, often from autoimmune destruction of gastric parietal cells or the intrinsic factor itself. Other conditions listed do not involve this specific absorption defect or the resulting abnormal red blood cell production caused by B12 deficiency, so pernicious anemia best fits the description.