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Pernicious Anemia and Other B Vitamin Deficiencies

Pernicious anemia is a condition in which the body doesn't absorb enough vitamin B12 to make enough red blood cells (RBCs). This happens when the body doesn't make enough of a substance called "intrinsic factor." Intrinsic factor is a protein produced by cells in the stomach lining that bind to vitamin B12 and allow it to be absorbed in the small intestine. Without enough intrinsic factor, the body cannot absorb vitamin B12 from the diet and cannot produce enough normal RBCs, which leads to anemia. In addition to lack of intrinsic factor, other causes of vitamin B12 deficiency and anemia include dietary deficiency and conditions that affect absorption of the vitamin from the small intestine such as surgery, certain drugs, digestive disorders (celiac disease, Crohn disease), and infections. Of these, pernicious anemia is the most common cause of B12 deficiency.

Vitamin B12 deficiency can result in general symptoms of anemia as well as nerve problems. These may include:

  • Numbness and tingling that start first in the hands and feet (from nerve damage)
  • Muscle weakness
  • Slow reflexes
  • Loss of balance
  • Unsteady walking
  • Confusion, memory loss, depression, and/or dementia in severe cases

Folic acid is another B vitamin, and deficiency in this vitamin may also lead to anemia. Folic acid, also known as folate, is found in many foods, especially in green, leafy vegetables. Folic acid is added to most grain products in the United States so that deficiency in folic acid is rarely seen in the U.S. nowadays. Folic acid is needed during pregnancy for normal development of the brain and spinal cord. It is important for women considering pregnancy to take appropriate amounts of folate supplements before they get pregnant and during pregnancy to make sure that they are not folate-deficient.

Anemia resulting from vitamin B12 or folate deficiency are often referred to as "megaloblastic anemia" because red blood cells are larger than normal. A lack of these vitamins does not allow RBCs to develop normally, which leads to their large size. This results in a reduced number of abnormally large RBCs and anemia.

Laboratory Tests
Symptoms of anemia will usually be investigated initially with a complete blood count (CBC) and differential. In pernicious anemia, other causes of vitamin B12 deficiency, or folate deficiency, these usually reveal:

  • A low hemoglobin level
  • Red cell indices—the mean corpuscular volume (MCV), which is the average size of RBCs, is high. Mean corpuscular hemoglobin (MCH) is also high, but mean corpuscular hemoglobin concentration (MCHC) is typically normal.
  • A blood smear will reveal RBCs that are abnormally large and oval-shaped.
  • The numbers of neutrophils (a type of white blood cell) and platelets may also be decreased.

Additional tests are usually done to make the diagnosis. Some of these include:

Sometimes a bone marrow aspiration or biopsy may be performed to see if the marrow appearance is consistent with megaloblastic anemia and to rule out other bone marrow disorders that may also cause anemia with larger RBCs.

Treatment in these conditions involves supplementation with the vitamin that is deficient. If the cause of deficiency is the inability to absorb vitamin B12 from the digestive tract, then the vitamin may be given as injections. Treatment of underlying causes such as a digestive disorder or infection may help to resolve the anemia.

For more on this, see the article on Vitamin B12 and Folate Deficiency.

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