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Vitamin B12 deficiency anemia

Megaloblastic macrocytic anemia; Cobalamin deficiency anemia

Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. There are many types of anemia.

Vitamin B12 deficiency anemia is a low red blood cell count due to a lack (deficiency) of vitamin B12.

Causes

Your body needs vitamin B12 to make red blood cells. In order to provide vitamin B12 to your cells:

  • You must eat foods that contain vitamin B12, such as meat, poultry, shellfish, eggs, fortified breakfast cereals, and dairy products.
  • Your body must absorb enough vitamin B12. A special protein, called intrinsic factor, helps your body do this efficiently. This protein is released by cells in the stomach.

Certain health conditions can make it difficult for your body to absorb enough vitamin B12. They include:

  • Pernicious anemia, a condition that occurs when your body destroys cells in your stomach that make intrinsic factor, which may lead to vitamin B12 deficiency and anemia
  • Surgery that removes certain parts of your stomach or small intestine, such as some weight-loss surgeries
  • Crohn disease, celiac disease, infection with the fish tapeworm, or other problems that make it difficult for your body to digest foods
  • Alcohol use
  • Taking antacids and other heartburn medicines for a long period of time
  • Abuse of laughing gas (nitrous oxide)
  • Long term use of the medicine metformin

A lack of vitamin B12 may be due to dietary factors, including:

  • Eating a strict vegetarian diet
  • Poor diet in infants
  • Poor nutrition during pregnancy

Symptoms

You may not have symptoms. Symptoms may be mild.

Symptoms may include:

If you have low vitamin B12 level for a long time, it can cause nerve damage. Symptoms of nerve damage include:

  • Numbness and tingling of hands and feet
  • Loss of balance
  • Problems concentrating
  • Confusion or change in mental status (dementia) in severe cases
  • Psychosis (losing contact with reality)
  • Hallucinations

Exams and Tests

The health care provider will perform a physical exam. This may reveal problems with your reflexes or sensations.

Tests that may be done include:

Other procedures that may be done include:

Treatment

Treatment depends on the cause of B12 deficiency anemia. The goal of treatment is to increase your vitamin B12 level.

For people who have a low level of B12 due to a restricted vegetarian diet, taking B12 pills may resolve the issue.

For people with a health condition that causes B12 deficiency, treatment may include a shot of vitamin B12, often once a month. If you have a very low level of B12, you may need more shots in the beginning. It is possible you may need shots regularly for the rest of your life.

Your provider will also recommend that you eat a variety of foods.

Outlook (Prognosis)

People with this type of anemia often do well with treatment.

Long-term vitamin B12 deficiency can cause nerve damage. This may be permanent if you do not start treatment promptly after your symptoms begin. If nerve damage is severe or long-lasting, some damage may be permanent.

Vitamin B12 deficiency anemia most often responds well to treatment. It will likely get better when the underlying cause of the deficiency is treated.

Possible Complications

A woman with a low B12 level may have a false positive Pap smear. This is because vitamin B12 deficiency affects the way certain cells (epithelial cells) in the cervix look.

When to Contact a Medical Professional

Contact your provider if you have any of the symptoms of anemia.

Prevention

Eating a well-balanced diet can help ensure you get enough vitamin B12 from the foods you eat. However, it can't prevent anemia in people with certain health conditions that prevent their body from using vitamin B12 properly.

Shots of vitamin B12 can prevent anemia if you've had a surgery known to cause vitamin B12 deficiency.

Early diagnosis and prompt treatment can reduce or prevent complications related to a low vitamin B12 level.

There is no evidence that taking B12 supplements will prevent or treat dementia, Alzheimer disease, or other health conditions such as heart disease.

Open References

References

Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 40.

Means Jr. RT. Approach to the anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 144.

National Institutes of Health website. Vitamin B12: fact sheet for health professionals. ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Updated March 26, 2024. Accessed August 17, 2024.

Stabler SP. Megaloblastic anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 150.

  • Anemia

    Animation

    •  

    Anemia - Animation

    Do you feel tired and listless? Do you find your mind drifting during the day? Do you get dizzy or short of breath whenever you climb the stairs? There are a few possible reasons for the way you feel, but you could have anemia. You could even have anemia without noticing any symptoms at all. Anemia is a problem with hemoglobin, a substance in red blood cells that carries oxygen throughout your body. Without enough hemoglobin, your heart and other organs can't get the oxygen they need to work. When your organs slow down, you slow down and you start feeling tired and listless. Many different health conditions can cause anemia, from heavy blood loss during a woman's period, to pregnancy, to an underactive thyroid gland. Healthy red blood cells are made in your bone marrow, the soft tissue in the middle of your bones. Any disease that damages blood marrow, such as lymphoma or leukemia, can also affect your red blood cell production. Anemia can also be caused by an immune system problem that damages red blood cells, or surgery to the stomach or intestines. How do you know if you have anemia? You may feel tired, dizzy, and have trouble concentrating. You may get sick more often. People with anemia often complain of chest pain, headaches, or shortness of breath. Your skin might look pale, like you haven't seen the sun for months. Because these can also be symptoms of other conditions, your doctor will confirm that you have anemia by taking a blood test to check your red blood cell count and hemoglobin level. Blood tests can also look for problems that may be causing your anemia, such as a vitamin or iron deficiency. If you are anemic, it's very important to treat it. When your body isn't getting enough oxygen, it can starve vital organs like your heart. This can lead to a heart attack. How you treat anemia really depends on the cause. If the problem is with your bone marrow, you may take a medicine called erythropoietin, which will help your bone marrow make more red blood cells. If the problem is a vitamin or mineral deficiency, your doctor may prescribe iron, vitamin B12, or folic acid supplements. Or, you may need a blood transfusion to replace damaged red blood cells with healthy ones. How well you do really depends on what's causing your anemia. Call your doctor if you have any symptoms like fatigue or shortness of breath. Once your doctor can find and treat the cause of your anemia, you should have more energy and start feeling like your old self again.

  • Megaloblastic anemia - view of red blood cells

    Megaloblastic anemia - view of red blood cells - illustration

    This picture shows large, dense, oversized, red blood cells (RBCs) that are seen in megaloblastic anemia. Megaloblastic anemia can occur when there is a deficiency of vitamin B-12.

    Megaloblastic anemia - view of red blood cells

    illustration

  • Hypersegmented PMN (Close-up)

    Hypersegmented PMN (Close-up) - illustration

    This image shows a large polymorphonuclear leukocyte (PMN) with multiple discretely-identifiable nuclear lobes. It can be seen in megaloblastic anemias. Normal PMN's have less than or equal to 5 lobes.

    Hypersegmented PMN (Close-up)

    illustration

  • Anemia

    Animation

    •  

    Anemia - Animation

    Do you feel tired and listless? Do you find your mind drifting during the day? Do you get dizzy or short of breath whenever you climb the stairs? There are a few possible reasons for the way you feel, but you could have anemia. You could even have anemia without noticing any symptoms at all. Anemia is a problem with hemoglobin, a substance in red blood cells that carries oxygen throughout your body. Without enough hemoglobin, your heart and other organs can't get the oxygen they need to work. When your organs slow down, you slow down and you start feeling tired and listless. Many different health conditions can cause anemia, from heavy blood loss during a woman's period, to pregnancy, to an underactive thyroid gland. Healthy red blood cells are made in your bone marrow, the soft tissue in the middle of your bones. Any disease that damages blood marrow, such as lymphoma or leukemia, can also affect your red blood cell production. Anemia can also be caused by an immune system problem that damages red blood cells, or surgery to the stomach or intestines. How do you know if you have anemia? You may feel tired, dizzy, and have trouble concentrating. You may get sick more often. People with anemia often complain of chest pain, headaches, or shortness of breath. Your skin might look pale, like you haven't seen the sun for months. Because these can also be symptoms of other conditions, your doctor will confirm that you have anemia by taking a blood test to check your red blood cell count and hemoglobin level. Blood tests can also look for problems that may be causing your anemia, such as a vitamin or iron deficiency. If you are anemic, it's very important to treat it. When your body isn't getting enough oxygen, it can starve vital organs like your heart. This can lead to a heart attack. How you treat anemia really depends on the cause. If the problem is with your bone marrow, you may take a medicine called erythropoietin, which will help your bone marrow make more red blood cells. If the problem is a vitamin or mineral deficiency, your doctor may prescribe iron, vitamin B12, or folic acid supplements. Or, you may need a blood transfusion to replace damaged red blood cells with healthy ones. How well you do really depends on what's causing your anemia. Call your doctor if you have any symptoms like fatigue or shortness of breath. Once your doctor can find and treat the cause of your anemia, you should have more energy and start feeling like your old self again.

  • Megaloblastic anemia - view of red blood cells

    Megaloblastic anemia - view of red blood cells - illustration

    This picture shows large, dense, oversized, red blood cells (RBCs) that are seen in megaloblastic anemia. Megaloblastic anemia can occur when there is a deficiency of vitamin B-12.

    Megaloblastic anemia - view of red blood cells

    illustration

  • Hypersegmented PMN (Close-up)

    Hypersegmented PMN (Close-up) - illustration

    This image shows a large polymorphonuclear leukocyte (PMN) with multiple discretely-identifiable nuclear lobes. It can be seen in megaloblastic anemias. Normal PMN's have less than or equal to 5 lobes.

    Hypersegmented PMN (Close-up)

    illustration

A Closer Look

 

Tests for Vitamin B12 deficiency anemia

 
 

Review Date: 3/31/2024

Reviewed By: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 08/19/2024.

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