Anemia - B12 deficiency

Anemia - B12 deficiency


B12 deficiency anemia is a drop in the number of red blood cells due to a lack of vitamin B12.

Alternative Names

Macrocytic anemia


Vitamin B12 is essential for normal nervous system function and blood cell production. The main sources of vitamin B12 include meat, eggs, and dairy products. For vitamin B12 to be absorbed by the body, it must bind to intrinsic factor, a protein secreted by cells in the stomach.

Causes of vitamin B12 deficiency include:

  • A diet low in vitamin B12 (for example, a strict vegetarian diet that excludes all meat, fish, dairy products, and eggs)
  • Chronic alcoholism
  • Abdominal or intestinal surgery that affects intrinsic factor production or absorption
  • Crohn's disease
  • Intestinal malabsorption disorders
  • Fish tape worm
  • Pernicious anemia, which is caused by a lack of intrinsic factor

The risk factors are related to the causes.


  • Loss of appetite
  • Diarrhea
  • Numbness and tingling of hands and feet
  • Paleness
  • Shortness of breath
  • Fatigue
  • Weakness
  • Sore mouth and tongue
  • Confusion or change in mental status in severe or advanced cases

Exams and Tests

A physical exam may show problems with reflexes or positive Babinski reflex.

The following tests will be done:

  • CBC
  • Bone marrow examination
  • LDH
  • Vitamin B12 level
  • Schilling test


Treatment depends on the specific cause of B12 deficiency anemia.

Pernicious anemia requires lifelong vitamin B12 injections. Those with anemia due to a lack of vitamin B12 may be told to take vitamin supplements and to follow a more balanced diet. It may be treated initially with vitamin B12 injections.

Anemia caused by malabsorption is treated with vitamin B12 injections until the condition improves.

Outlook (Prognosis)

Treatment for this form of anemia is usually effective.

Possible Complications

  • The signs and symptoms related to the central nervous system may be irreversible if treatment is not begun within 6 months of when these symptoms begin.
  • Vitamin B12 affects epithelial cells (cells that form the outer surface of the body and line inner passageways). Therefore, a lack of B12 may cause a false-positive Pap smear.

When to Contact a Medical Professional

Call your health care provider if you have any of the symptoms of anemia.


Anemia caused by a lack of vitamin B12 can be prevented by following a well-balanced diet. B12 injections can prevent anemia after surgeries known to cause vitamin B12 deficiency. Early diagnosis and prompt treatment can limit the severity and complications of this anemia.

Chapman IM. Nutritional disorders in the elderly. Med Clin North Am. Sept 2006; 90(5): 887-907.

Rakel RE. Textbook of Family Practice. 6th ed. Philadelphia, Pa: WB Saunders; 2005:1232.

Anemia - B12 deficiency
Alcohol abuse
Acute kidney failure
HELLP syndrome
Colorectal polyps
Papillary carcinoma of the thyroid
Traumatic nasogastric or endotracheal intubation
Allergic dermatitis
Acute brain syndrome
Actinic keratosis

Copyright by 2006-2023. All rights reserved