Anemia - B12 deficiency

Alternative names
Macrocytic anemia


Anemia is a drop in the number of red blood cells. This can be caused by a lack of Vitamin B12.

Causes, incidence, and risk factors

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 excluding 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.


Signs and tests
A physical evaluation of the patient’s neurological signs may show depressed deep tendon reflexes, decreased position sense, decreased vibration sense, or positive Babinski reflex. Other signs and tests include the following:

  • CBC results show low hematocrit with an elevated MCV  
  • Bone marrow examination  
  • Elevated LDH  
  • Below-normal Vitamin B12 level  
  • Schilling test (to determine where the deficiency in B12 absorption lies).


Treatment depends on the cause of the anemia:

Expectations (prognosis)

Treatment for this form of anemia is usually effective.


  • 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 a lack of B12 may cause a false positive Pap smear.

Calling your health care provider
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 through a well-balanced diet. Preventative use of Vitamin B12 injections can prevent anemia after surgeries known to cause vitamin B12 deficiency. Early diagnosis and prompt treatment can limit the severity of this anemia as well as the neurologic complications.

Johns Hopkins patient information

Last revised: December 4, 2012
by Harutyun Medina, M.D.

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