Pernicious anemia is a decrease in red blood cells that occurs when the body cannot properly absorb vitamin B12 from the gastrointestinal tract. Vitamin B12 is necessary for the proper development of red blood cells.
Pernicious anemia is a type of megaloblastic anemia.
See also: Anemia
Macrocytic achylic anemia; Congenital pernicious anemia; Juvenile pernicious anemia; Vitamin B12 deficiency (malabsorption)
Causes, incidence, and risk factors
The body needs vitamin B12 to make red blood cells. To provide vitamin B12 to your blood cells, you need to eat enough foods containing vitamin B12, such as meat, poultry, shellfish, eggs, and dairy products.
To absorb vitamin B12, your body uses a special protein called intrinsic factor, which is released by cells in the stomach. The combination of vitamin B12 bound to intrinsic factor is absorbed in the last part of the small intestine.
When the stomach does not make enough intrinsic factor, the intestine cannot properly absorb vitamin B12.
Very rarely, infants and children are born without the ability to produce enough intrinsic factor, or the ability to absorb the combination of intrinsic factor and vitamin B12 in the small intestine. Pernicious anemia that occurs at birth (congenital) is inherited. You need the defective gene from each parent to get it.
Common causes of pernicious anemia include:
- Weakened stomach lining (atrophic gastritis)
- The body's immune system attacking the cells that make intrinsic factor (autoimmunity against gastric parietal cells) or intrinsic factor itself
The disease begins slowly and may take decades to fully establish. Although the congenital form occurs in children, pernicious anemia usually does not appear before age 30 in adults. The average age at diagnosis is 60.
Risk factors include:
- Family history of the disease
- History of autoimmune endocrine disorders, including:
- Scandinavian or Northern European descent
See also: Anemia - B12 deficiency for other causes of low vitamin B12 levels.
People with mild anemia may have no symptoms or very mild symptoms. More typical symptoms of vitamin B12 deficiency anemia include:
- Diarrhea or constipation
- Fatigue, lack of energy, or light-headedness when standing up or with exertion
- Loss of appetite
- Pale skin
- Problems concentrating
- Shortness of breath, mostly during exercise
- Swollen, red tongue or bleeding gums
- Nerve damage caused by vitamin B12 deficiency that has been present for a longer time may cause:
Signs and tests
Tests that may used to diagnose or monitor pernicious anemia include:
- Bone marrow examination (only needed if diagnosis is unclear)
- Complete blood count (CBC)
- Measurement of serum holotranscobalamin II
- Reticulocyte count
- Schilling test
- Serum LDH
- Serum methylmalonic acid (MMA) level
- Serum vitamin B12 level
Pernicious anemia may also affect the results of the following tests:
Vitamin B12 deficiency affects the appearance of cells that form on the outer surface of the body and line inner passageways (epithelial cells). An untreated woman may have a false positive Pap smear.
Monthly vitamin B12 injections are prescribed to correct the vitamin B12 deficiency. This therapy treats the anemia and may correct the neurological complications if taken early enough. In people with a severe deficiency, the injections are given more often at first.
Some doctors recommend that elderly patients with gastric atrophy take vitamin B12 supplements by mouth in addition to monthly injections.
There is also a preparation of vitamin B12 that may be given through the nose. For some people, taking vitamin B12 tablets by mouth in a very high dose can be an effective treatment.
The outcome is usually excellent with treatment.
Any damage to nerves may be permanent, especially if treatment is not started within 6 months of when symptoms began.
People with pernicious anemia may have gastric polyps, and they are at increased risk for gastric cancer and gastric carcinoid tumors.
Brain and nervous system (neurological) problems may continue if treatment is delayed.
Calling your health care provider
Call your health care provider if you have symptoms of vitamin B12 deficiency.
There is no known way to prevent this condition. However, with early detection and treatment of vitamin B12 deficiency, complications can be minimized.
Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Shattil SS, et al., eds. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2008:chap 39.
Reviewed By: David Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Aslo reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.