What is pernicious anemia?

• A. A B12 deficiency caused by a lack of intrinsic factor
• B. A deficiency caused by iron overload
• C. A deficiency of folate (Vitamin B9)
• D. An autoimmune destruction of platelets

Answer: (A)

Pernicious anemia is a form of megaloblastic anemia caused by vitamin B12 deficiency due to lack of intrinsic factor, which is needed to absorb B12 in the gut. This lack is usually autoimmune, with destruction of gastric parietal cells or antibodies against intrinsic factor, leading to inadequate B12 absorption despite a normal or adequate B12 intake. Without enough B12, DNA synthesis in hematopoietic cells falters, producing macrocytic, ineffective red blood cell production and often neurologic symptoms from demyelination. Treatment involves replacing B12, typically with injections or high-dose oral B12, and addressing the underlying autoimmune gastritis. The other options describe different issues: iron overload is a separate condition, folate deficiency also causes macrocytic anemia but not from intrinsic factor deficiency, and autoimmune destruction of platelets is separate (ITP).