Pernicious Anemia and Other B Vitamin Deficiencies
Pernicious anemia is a condition in which the body does not make enough of a substance called "intrinsic factor." Intrinsic factor is a protein produced by parietal cells in the stomach that binds to vitamin B12 and allows it to be absorbed from the small intestine. Vitamin B12 is important in the production of red blood cells (RBCs). Without enough intrinsic factor, the body cannot absorb vitamin B12 from the diet and cannot produce enough normal RBCs, leading 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 symptoms.
Vitamin B12 deficiency can result in general symptoms of anemia as well as nerve problems. These may include:
- Weakness or fatigue
- Lack of energy
- Numbness and tingling that start first in the hands and feet
Additional symptoms may include muscle weakness, slow reflexes, loss of balance and unsteady walking. Severe cases can lead to confusion, memory loss, depression, and/or dementia.
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. today. Folic acid is needed during pregnancy for normal development of the brain and spinal cord. It is important for women considering pregnancy to take folate supplements before they get pregnant and during pregnancy to make sure they are not folate deficient. Folate deficiency early in pregnancy can cause problems in the development of the brain and spinal cord of the baby.
Anemias resulting from vitamin B12 or folate deficiency are sometimes referred to as "macrocytic" or "megaloblastic" anemia because red blood cells are larger than normal. A lack of these vitamins does not allow RBCs to grow and then divide as they normally would during development, which leads to their large size. This leads to 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 or vitamin B12 deficiency, these usually reveal:
- A low hemoglobin level
- For red cell indices, the mean corpuscular volume (MCV), which is the average size of RBCs, is often high.
- A blood smear will reveal red blood cells that are abnormally large.
Folic acid deficiency can cause the same pattern of changes in hemoglobin and red cell size as vitamin B12 deficiency. If the cause of your anemia is thought to be due to pernicious anemia or dietary deficiency of B12 or folate, additional tests are usually done to make the diagnosis. Some of these include:
- Vitamin B12 level—blood level may be low when deficient in B12
- Folic acid level—blood level may be low if deficient in this B vitamin
- Methylmalonic acid (MMA)—may be high with vitamin B deficiency
- Homocysteine—may be high with either folate or vitamin B deficiency
- Reticulocyte count—is usually low
- Antibodies to intrinsic factor or parietal cell antibodies—may be present in pernicious anemia
Sometimes a bone marrow aspiration may be performed. This may reveal larger than normal sizes in the cells that eventually mature and become RBCs (precursors).
Treatment in these conditions involves supplementation with the vitamin that is deficient. If the cause of deficiency is the inability to absorb the vitamin 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.
