Pernicious anemia (PA) is an autoimmune disorder in which the body fails to make enough healthy red blood cells (RBCs). The body requires vitamin B-12 and a type of protein called intrinsic factor (IF) to make red blood cells. Vitamin B-12, or cobalamin, is found in certain foods and medications. IF is a protein made by the stomach’s mucosal (mucus-secreting) cells, called parietal cells. When vitamin B-12 enters the body, it binds with IF. The two are then absorbed in the last part of the small intestine.
In the majority of cases of PA, the body’s immune system attacks and destroys the stomach’s mucosal cells. IF can no longer be made, and vitamin B-12 cannot be absorbed.
Vitamin B-12 deficiency produces a small number of overly large and ineffective RBCs called macrocytes. Because of their large size, these cells may not be able to leave the bone marrow and enter the bloodstream. The resulting decrease in oxygen-carrying RBCs in the bloodstream can lead to fatigue and weakness.
According to the National Heart, Lung, and Blood Institute (NHLBI), this type of anemia is called “pernicious” because it was once considered a deadly disease. This was due to the lack of available treatment. Today, the disease is relatively easy to treat with B-12 shots or supplements. (NHLBI, 2001)
However, untreated vitamin B-12 deficiency can lead to more severe complications such as neurological problems, chronic anemia, and stomach cancer.
PA is a type of macrocytic anemia and is sometimes called megaloblastic anemia because of the large size of the red blood cells produced. Anemia is a medical condition in which the blood is low in normal red blood cells.
Macrocytic anemia is not unique to PA and can have other causes including:
- long-term use of certain medications and antibiotics (methotrexate, azathioprine, etc.)
- chronic obstructive pulmonary disease (COPD)
- folate deficiency caused by poor intake or malabsorption
Other causes of vitamin B-12 deficiency are often confused with PA. PA is strictly an autoimmune disorder resulting from a lack of IF. According to the NHLBI, PA is also seen in children who are born with a genetic defect which prevents them from making IF. (NHLBI, 2011)
The progression of PA is very slow, making it difficult for patients to recognize symptoms because they have grown accustomed to feeling “unwell.”
Commonly overlooked symptoms include:
- chest pain
- weight loss
In rare cases of PA, patients may display neurological symptoms including:
A diagnosis of PA requires several different tests. It requires a:
- complete blood count (CBC) test
- vitamin B-12 deficiency test
- IF deficiency test
- proof of stomach destruction
CBC measures the amount of:
- hemoglobin - protein bound to oxygen to carry it throughout the blood
- hematocrit - used to measure how much space red blood cells use within the blood
Vitamin B-12 levels are assessed through a blood test. Low levels indicate a deficiency.
Damage to the stomach walls is easily diagnosed through a biopsy. A biopsy removes a sample of the stomach’s cells. The cells are examined microscopically for damage.
Intrinsic factor deficiency is tested through a blood sample. The blood is tested for antibodies against IF and the stomach’s mucosal cells.
In a healthy immune system, antibodies are responsible for finding bacteria or viruses. They then mark the invading germs for destruction. In an autoimmune disease, such as PA, the body’s antibodies stop distinguishing between disease and healthy tissue. In this case, they demolish the cells making IF.
The treatment for PA is a two-part process:
- first, treat any existing vitamin B-12 deficiency and check for iron-deficiency
- second, lifelong surveillance for long-term consequences
Treatment begins with:
- vitamin B-12 injections that are slowly decreased over time
- blood test for iron deficiency followed by regular blood tests
- CBC tests to measure serum cobalamin and ferritin levels
- blood tests to monitor replacement treatments
Symptoms of long-term damage include:
- upset stomach
- difficulty swallowing
- weight loss
- iron deficiency
Lifelong surveillance focuses on identifying serious consequences. The most dangerous is gastric cancer. Studies have shown a link between damage done to the stomach’s lining by PA and gastric cancer. Regular visits and biopsies are able to check for the beginnings of cancer.