Anemia is a medical condition in which the blood is low in normal red blood cells.

Pernicious anemia is one cause of vitamin B12 deficiency anemia. It’s thought to mainly be caused by an autoimmune process that makes a person unable to produce a substance in the stomach called intrinsic factor.

This substance is needed to absorb dietary vitamin B12 in the small intestine. Vitamin B12 is a required nutrient that helps allow proper red blood cell production and function in the body.

Pernicious anemia is a rare condition. It occurs in 0.1 percent of the general population and 1.9 percent in people who are older than 60 years, according to a 2012 study in the Journal of Blood Medicine.

However, up to 50 percent of anemia from vitamin B12 deficiency in adults is caused by pernicious anemia, study authors note.

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 condition is relatively easy to treat with vitamin B12 injections or possibly oral supplementation. If left untreated, vitamin B12 deficiency due to any cause can lead to severe complications.

The progression of pernicious anemia is typically slow. It may be difficult to recognize the symptoms because you may have become used to not feeling well.

Common symptoms include:

In more severe or prolonged cases of vitamin B12 deficiency, including cases due to pernicious anemia, people may have neurological symptoms. These can include:

Other symptoms of vitamin B12 deficiency, including that due to pernicious anemia, include:

Pernicious anemia involves autoimmune inflammation in the stomach and the inability to absorb vitamin B12 in the small intestine.

While vitamin B12 deficiency anemia may be caused by a lack of vitamin B12 in the diet, pernicious anemia is caused by an inability to absorb vitamin B12.

There are two causes of pernicious anemia: autoimmune and genetic.

Pernicious anemia occurs when the stomach can’t make intrinsic factor and the small intestine can’t absorb vitamin B12 from in the diet, including from foods.

Pernicious anemia is sometimes seen in association with certain autoimmune endocrine diseases, including:

  • type 1 diabetes mellitus
  • hypoparathyroidism
  • Addison’s disease
  • Graves’ disease

In most cases of pernicious anemia, the body’s immune system attacks and destroys the cells, known as parietal cells, that produce intrinsic factor in the stomach.

Risk factors for pernicious anemia

Some people are more likely than others to develop pernicious anemia.

Risk factors include:

  • having a family history of the disease
  • being of Northern European or Scandinavian descent
  • having type 1 diabetes mellitus, or other specific autoimmune conditions
  • having had part of your stomach removed
  • being 60 years or older

Your risk of developing pernicious anemia also increases as you age.

Other vitamin B12 deficiencies, such as those caused by dietary intake, are often confused with pernicious anemia.

Pernicious anemia is mainly thought to be an autoimmune disorder that hurts the parietal cells in the stomach and inhibits the proper functioning of intrinsic factor.

However, pernicious anemia may also have a genetic component to it as well. It may potentially run in families. There are also children with pernicious anemia who are born with a genetic defect that prevents them from making intrinsic factor.

Pernicious anemia and other vitamin B12 deficiency anemia due to small intestinal malabsorption can be treated with an intramuscular B12 injection by your physician.

High-dose oral vitamin B12 supplementation may be an effective option for some people with pernicious anemia as well.

In people with vitamin B12 deficiency anemia where the body can absorb vitamin B12, oral vitamin B12 supplementation and diet adjustments may be an effective treatment.

Risk factors for vitamin B12 deficiency from other causes

The risk factors for developing vitamin B12 deficiency from other causes include:

  • lack of intrinsic factor in the body
  • problems in the small intestine
  • other causes of inflammation in the stomach lining (atrophic gastritis)
  • gastrectomy, where surgery removes part or all of the stomach
  • gastrointestinal tract infection
  • long-term use of anti-acid medication

Vitamin B12 plays a role in creating red blood cells. The body requires an adequate intake of vitamin B12, which can be found in foods like:

  • meat
  • eggs
  • fortified nondairy milks (soy, nut, and rice)

Your body also needs a type of protein called intrinsic factor to absorb vitamin B12. Intrinsic factor is a protein produced by the parietal cells in the stomach.

After you consume vitamin B12, it travels to your stomach where intrinsic factor binds to it. The two are then absorbed in the last part of your small intestine.

Diseases within the small intestine can cause vitamin B12 deficiency to develop. These diseases can include:

Vitamin B12 deficiency can also occur if the ileum portion of the small intestine is surgically removed.

Disruption within the normal flora bacteria of the small intestine may also lead to vitamin B12 deficiency. Antibiotics may cause a deficiency of bacteria needed to maintain proper intestinal absorption.

Other people may have too many small intestinal bacteria that cause malabsorption and a deficiency of vitamin B12 as well.

Your doctor will usually need to do several tests to diagnose pernicious anemia, such as:

  • Complete blood count. This test can screen for an anemia in general by looking at such things as hemoglobin and hematocrit levels.
  • Vitamin B12 level. If vitamin B12 deficiency is suspected as the cause of your anemia, your doctor can assess your vitamin B12 level through this type of blood test. A lower than normal level indicates a deficiency.
  • Intrinsic factor and parietal cell antibodies. The blood is tested for antibodies against intrinsic factor and the stomach’s parietal 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 pernicious anemia, the body’s immune system stops distinguishing between diseased and healthy tissue. In this case, autoantibodies destroy the stomachs cells that make intrinsic factor and impede its function.

The treatment for pernicious anemia is a two-part process. Your doctor will treat any existing vitamin B12 deficiency.

Treatment of pernicious anemia usually consists of:

  • vitamin B12 injections that are followed closely over time
  • following the blood level of vitamin B12 over the course of therapy
  • making adjustments accordingly in vitamin B12 dosing

Vitamin B12 injections can be given daily or weekly until the B12 levels return to a healthy range. During the first few weeks of treatment, your doctor may recommend limiting physical activity.

After your vitamin B12 levels get in range, you may only need to get the shot once per month. You may be able to administer the shots yourself or have someone else give them to you at home to save trips to the doctor.

After your vitamin B12 level is in a healthy range, your doctor may recommend you take oral doses of B12 supplements instead of the injection.

However, depending on your intrinsic factor deficiency — where you may have poor intestinal absorption of vitamin B12 — vitamin B12 injections may be needed as your sole treatment of pernicious anemia.

Your doctor will likely want to see you on a long-term basis. This will help them identify possible serious effects of pernicious anemia.

A dangerous potential complication is gastric cancer. Your doctor can monitor you for symptoms of cancer at regular visits and through imaging and biopsies, if needed.

Other potential complications of pernicious anemia include:

These complications most often stem from long lasting pernicious anemia. They can be permanent, but effective management is possible.

Many people with pernicious anemia require long-term treatment and monitoring. This can help prevent damage from setting in to different body systems.

Talk with your doctor if you think you may have symptoms of pernicious anemia. The earlier you get a diagnosis and start treatment and monitoring, the better your outcome for preventing any future problems.