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Pernicious Anemia

Pernicious anemia is a condition in which the body can't make enough healthy red blood cells because it doesn't have enough vitamin B12.

Vitamin B12 is a nutrient found in certain foods. The body needs this nutrient to make healthy red blood cells and to keep its nervous system working properly.


Vitamin B12 deficiency may lead to nerve damage. This can cause tingling and numbness in your hands and feet, muscle weakness, and loss of reflexes. You also may feel unsteady, lose your balance, and have trouble walking.

Severe vitamin B12 deficiency can cause neurological problems, such as confusion, dementia, depression, and memory loss. Other symptoms of vitamin B12 deficiency involve the digestive tract. These symptoms include nausea (feeling sick to your stomach) and vomiting, heartburn, abdominal bloating and gas, constipation or diarrhea, loss of appetite, and weight loss. An enlarged liver is another symptom.

A smooth, beefy red tongue also is a sign of vitamin B12 deficiency and pernicious anemia.

Infants who have vitamin B12 deficiency may have poor reflexes or unusual movements, such as face tremors. They may have trouble feeding due to tongue and throat problems. They also may be irritable. If vitamin B12 deficiency isn't treated, infants can have permanent growth problems.


Complete Blood Count

Often, the first test used to diagnose many types of anemia is a complete blood count (CBC). This test measures many different parts of your blood, including mean corpuscular volume (MCV). MCV is a measure of the average size of your red blood cells. MCV can be a clue as to what's causing your anemia. In pernicious anemia, the red blood cells are larger than normal (macrocystic).

A reticulocyte count measures the number of young red blood cells in your blood. The test shows whether your bone marrow is making red blood cells at the correct rate. People who have pernicious anemia have low reticulocyte counts.

Other Blood Tests
  • Your vitamin B12 blood level. A low vitamin B12 level indicates pernicious anemia.
  • Your homocysteine and methylmalonic acid (MMA) levels. High levels of these substances in your body are a sign of pernicious anemia.
  • For intrinsic factor antibodies and parietal cell antibodies. These antibodies also are a sign of pernicious anemia.
Bone Marrow Tests

Bone marrow tests can show whether your bone marrow is healthy and making enough red blood cells. The two bone marrow tests are aspiration and biopsy.

For aspiration, your doctor removes a small amount of fluid bone marrow through a needle. For a biopsy, your doctor removes a small amount of bone marrow tissue through a larger needle. The samples are then examined under a microscope.

In pernicious anemia, the bone marrow cells that turn into blood cells are larger than normal (macrocystic).


Pernicious anemia is due to a lack of intrinsic factor or other causes, such as infections, surgery, medicines, or diet.

Lack of Intrinsic Factor

Intrinsic factor is a protein made in the stomach that helps your body absorb vitamin B12. In some people, lack of intrinsic factor is due to an autoimmune response.

An autoimmune response occurs when the immune system makes antibodies (proteins) that mistakenly attack and damage the body's tissues or cells. In pernicious anemia, the body makes antibodies that attack and destroy the parietal cells. These are the cells in the lining of the stomach that make intrinsic factor. Why this autoimmune response occurs isn't known. As a result of this attack, the stomach stops making intrinsic factor. Without intrinsic factor, your body can't move vitamin B12 through the small intestine, where it's absorbed. This leads to vitamin B12 deficiency.

A lack of intrinsic factor also can occur if you've had part or all of your stomach removed. This type of surgery reduces the number of parietal cells available to make intrinsic factor.

Rarely, children are born with an inherited disorder that prevents their bodies from making intrinsic factor. This disorder is called congenital pernicious anemia.

Other Causes

Besides a lack of intrinsic factor, other conditions and factors also can cause pernicious anemia.

Malabsorption in the Small Intestine

Sometimes pernicious occurs because the body's small intestine can't properly absorb vitamin B12. This may be the result of:

  • Too many of the wrong kind of bacteria in the small intestine. This is a common cause of pernicious anemia in older adults. The bacteria use up the available vitamin B12 before the small intestine can absorb it.
  • Diseases that interfere with vitamin B12 absorption. One example is celiac disease. This is a genetic disorder in which your body can't tolerate a protein called gluten. Another example is Crohn's disease. This is an inflammatory bowel disease.
  • Certain medicines that alter bacterial growth or prevent the small intestine from properly absorbing vitamin B12. Examples include antibiotics and certain diabetes and seizure medicines.
  • Surgical removal of part or all of the small intestine.
  • A tapeworm infection. The tapeworm feeds off the vitamin B12. Eating undercooked, infected fish may cause this type of infection.


Less often, people develop pernicious anemia because they don't get enough vitamin B12 in their diets. The best food sources for vitamin B12 are meat, poultry, fish, eggs, and dairy products. You also can get vitamin B12 from dietary supplements.

Strict vegetarians who don't eat any animal or dairy products and don't take a vitamin B12 supplement are at risk for pernicious anemia.

Breastfed infants of strict vegetarian mothers also are at risk for pernicious anemia. These infants can develop anemia within months of being born. This is because they haven't had enough time to store vitamin B12 in their bodies. Doctors treat these infants with vitamin B12 supplements.

Other groups, such as the elderly and people who suffer from alcoholism, also may be at risk for pernicious anemia because they may not get the proper nutrients in their diets.


Pernicious anemia usually is easy to treat with vitamin B12 shots or pills.

If you have severe pernicious anemia, your doctor may recommend shots first. Shots usually are given in a muscle every day or every week until the level of vitamin B12 in your blood improves. After your vitamin B12 blood level returns to normal, you may get a shot only once a month.

For less severe pernicious anemia, your doctor may recommend large doses of vitamin B12 pills. A vitamin B12 nose gel and spray also are available. These products may be useful for people who have trouble swallowing pills, such as older people who have had strokes.

Your signs and symptoms may begin to improve within a few days after the start of treatment. Your doctor may advise you to limit your physical activity until your condition improves.

If you have pernicious anemia due to a condition or factor other than lack of intrinsic factor, you may get treatment for the cause (if it can be found).

For example, medicines may be used to treat conditions that prevent your body from absorbing vitamin B12. If medicines are the cause of your pernicious anemia, your doctor may change the type or dose of medicine you take. Infants of strict vegetarian mothers may be given vitamin B12 supplements from birth.



National Heart, Lung, and Blood Institute, USA.