What defines pernicious anemia?

Pernicious anemia is specifically characterized by a low level of intrinsic factor, which is a protein produced by the stomach necessary for the absorption of vitamin B12 in the intestines. Without sufficient intrinsic factor, the body cannot effectively absorb vitamin B12 from food, leading to a deficiency of this crucial vitamin. Vitamin B12 is vital for the formation of red blood cells and the maintenance of the nervous system. The result of this malabsorption is megaloblastic anemia, where the red blood cells cannot mature properly and are larger than normal, leading to various symptoms, including fatigue, weakness, and neurological issues.

Other options mention deficiencies of different vitamins or minerals, which relate to other types of anemia but do not address the specific mechanism behind pernicious anemia, namely the role of intrinsic factor in vitamin B12 absorption.