Pernicious anemia is a deficiency of the B12 vitamin. Vitamins do not provide nutrition to the body on their own, rather they work with food or other elements in the body such as bacterias and enzymes to help the body work properly. Their absorption is also affected by other substances in the body, some that are already there, and some that people may ingest. In order to absorb vitamin B12, the body uses a substance called intrinsic factor, which is produced by the stomach. Some people's bodies either do not produce intrinsic factor at all, or they do not produce enough to effectively process vitamin B12 taken through food sources (like milk) or oral supplements. Older people may suffer from pernicious anemia even if they did not have it earlier in life, because as we age, our bodies produce less intrinsic factor. Also, more women than men suffer from it. People with pernicious anemia have to receive B12 by injection, because this form does not require combination with intrinsic factor to be absorbed by the body. People can also suffer from B12 deficiency unrelated to intrinsic factor problems, and this is called macrocytic anemia. It can be caused by poor diet, alcoholism, or metabolic disorders.

Symptoms of pernicious anemia include fatigue, diarrhea, rapid heart rate, and shortness of breath. While these symptoms fit a large range of maladies, people with pernicious anemia may also exhibit the Babinski reflex. When you stroke the bottom of the foot, the big toe flexes up and the other toes fan out. It is a reflex present in newborns and usually disappears by the age of 2, as the nervous system matures. When the reflex exists in older people, it can be a sign of nerve damage. It can be inherited, and is rarely diagnosed until age 30. All anemia is characterized by lower than normal numbers of red blood cells. There are several different types of anemia with different causes. Common anemias you may be familiar with are anemia caused by iron deficiency, and sickle cell anemia, where red blood cells are sickle, or crescent moon shaped and can stick together, causing fatigue and other symptoms. In pernicious anemia, patients have a low red blood cell count, but the red blood cells they do have are abnormally large, and their white blood cells have abnormally large nuclei. Further tests for antibodies against intrinsic factor can be performed to make a diagnosis of pernicious anemia.