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About Our Vitamin B12 Test

Vitamin B12, also known as Cobalamin, is an important vitamin for various areas of health, such as brain and nerve function, red blood cell production, cell and tissue repair, and DNA synthesis. Vitamin B12 deficiency can cause anemia (low levels of red blood cells) and damage to the nervous system. 

This blood test measures vitamin B12 levels to detect a deficiency. It is used to help diagnose one cause of anemia or neuropathy, evaluate nutritional status, and monitor the effectiveness of treatment for vitamin B12 deficiency. 

It may be ordered if you are experiencing symptoms associated with deficiency, if a complete blood count (CBC) has determined you have large red blood cells (RBCs), or if you have a condition associated with malabsorption. 

Signs of Low Vitamin B12

Low levels of vitamin B12 can cause:

  • Weakness
  • Fatigue
  • Pale skin
  • Prickling sensations/numbness in the hands and feet
  • Changes in balance and coordination
  • Loss of appetite
  • Constipation
  • Weight loss
  • Mood changes
  • Permanent nerve damage
  • Deteriorated brain function
  • Memory loss

Food Sources of Vitamin B12

Vitamin B12 is found in a variety of animal products.

You get Vitamin B12 by eating foods such as:

  • Fish
  • Meat
  • Poultry
  • Eggs
  • Dairy products
  • Some fortified breakfast cereals and nutritional yeast products 

Vitamin B12 is generally not found in plant foods.

People at Risk for Vitamin B12 Deficiency

Researchers believe that up to 15% of Americans have vitamin B-12 deficiency. 

Vitamin B12 deficiency is prevalent in:

  • People with a family history of vitamin B12 deficiency anemia
  • Older adults, who do not have enough hydrochloric acid in their stomach
  • Vegans or strict vegetarians
  • People who lack intrinsic factor 
  • People who had removal or bypass surgery of the stomach or small intestine
  • People who have conditions that interfere with nutrient absorption, such as Celiac disease or Crohn's disease
  • People who take certain medicines 

What Do Vitamin B12 Results Mean?


Low vitamin B12 levels can indicate:

  • Inadequate absorption 
  • Certain medications, such as Metformin and proton pump inhibitors used to treat acid reflux 
  • Dietary deficiencies
  • Increased need with a variety of diseases/conditions, such as pregnancy

If a vitamin B-12 deficiency is detected, you should talk to a care provider about your results. Treatment may involve changes to your diet, vitamin B-12 supplements, or (in severe cases) vitamin B-12 injections.


An increased level in vitamin B12 is unusual. This is because vitamin B-12 is a water-soluble vitamin, and excesses are usually removed in the urine. 

Increased vitamin B12 are associated with:

  • Recent ingestion/injection of vitamin B12 supplements
  • Liver disease
  • Kidney disease
  • Certain forms of leukemia

Vitamin B12 Deficiency Anemia

You need vitamin B12 to make healthy red blood cells, which transport oxygen throughout your body. When you lack Vitamin B12, blood cell production is affected. By extension, your tissues and organs don’t get enough oxygen, which means your body can’t function normally. 

Vitamin B12 deficiency is a common cause of megaloblastic anemia, in which the bone marrow produces abnormally large, unusually structured, and immature red blood cells. Pernicious anemia is a type of megaloblastic anemia in which a person can’t properly absorb vitamin B12 because they can’t produce intrinsic factor.

Low levels of either vitamin B12 and folate (another B vitamin) can cause macrocytic anemia, a condition in which blood cells are larger than normal and have low hemoglobin (the protein that carries oxygen). Macrocytic anemia makes a person feel weak and tired. 

Vitamin B12 deficiency anemia and folate deficiency anemia often occur together, and they can be hard to tell apart because they share similar symptoms. Taking high levels of folate can mask low levels of vitamin B12 by preventing anemia, although there is still an underlying problem. This is why vitamin B12 and folate are sometimes tested together.


  1. “Vitamin B12.” National Institutes of Health. https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/
  2. “Vitamin B12 deficiency can be sneaky, harmful.” Harvard Health Publishing. https://www.health.harvard.edu/blog/vitamin-b12-deficiency-can-be-sneaky-harmful-201301105780
  3. “Vitamin B12 Deficiency Anemia.” John Hopkins Medicine. https://www.hopkinsmedicine.org/health/conditions-and-diseases/vitamin-b12-deficiency-anemia

“Vitamin B12 and Folate.” LabCorp. https://www.labcorp.com/help/patient-test-info/vitamin-b12-and-folate

Medically Reviewed by: 2019-11-09

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