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A vitamin B-12 level test checks the amount of vitamin B-12 in the blood or urine to gauge the body’s overall vitamin B-12 stores. Levels will usually be between 200 and 900 picograms per milliliter, but the way of measuring will depend on the laboratory.

Vitamin B-12 is necessary for several bodily processes, including nerve function and the production of DNA and red blood cells.

A person whose vitamin B-12 levels are outside of the normal range will require treatment. Low levels of the vitamin can cause neurological symptoms, as well as fatigue, constipation, and weight loss. High B-12 levels may indicate liver disease, diabetes, or another condition.

Read on to learn more about testing B-12 levels and what the test results mean.

The vitamin B-12 level test checks how much vitamin B-12 is in the body. The results can help doctors to determine if abnormal vitamin B-12 levels are causing symptoms.

A doctor may order a vitamin B-12 level test if a person has any of the following:

Suspected vitamin B-12 deficiency

Researchers believe that up to 15 percent of people in the United States have vitamin B-12 deficiency. Signs and symptoms of deficiency include:

  • confusion
  • dementia
  • depression
  • difficulty maintaining balance
  • fast heartbeat
  • numbness and tingling in the hands and feet
  • poor memory
  • a sore mouth or tongue

Infants with vitamin B-12 deficiency may fail to thrive. They may experience movement problems in addition to delayed development.

Pernicious anemia

People with symptoms of pernicious anemia may also need a vitamin B-12 level test. Pernicious anemia, which causes low levels of red blood cells, results from an inability to absorb vitamin B-12.

It often affects older adults or those who are lacking intrinsic factor. Intrinsic factor is a substance in the stomach that binds to vitamin B-12 so that the body can absorb it.

Symptoms of pernicious anemia include:

  • constipation
  • fatigue
  • loss of appetite
  • pale skin
  • weakness
  • weight loss

High serum folate levels

Serum folate is the level of folic acid in the blood. High serum folate levels can mask the symptoms of vitamin B-12 deficiency and make its neurological symptoms worse.

They can also increase the likelihood of anemia.

Symptoms of other conditions

An abnormally high vitamin B-12 status can be an early sign of liver disease, diabetes, or certain types of leukemia. A doctor may use the results of a vitamin B-12 test to help form their diagnosis.

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Children and older adults are more likely to experience low vitamin B-12 levels.

Certain people are more at risk of vitamin B-12 deficiency than others, especially those who have low stomach acid or other digestive issues. Stomach acid separates vitamin B-12 from food so that the body can absorb it more efficiently.

The following groups of people are more likely than others to experience low vitamin B-12 levels:

  • older adults
  • children
  • vegans and vegetarians
  • people with diabetes
  • people with conditions that reduce vitamin B-12 absorption, including celiac disease and Crohn’s disease
  • people who have had gastric bypass surgery
  • those who are breast-feeding
  • people who are taking medicines such as chloramphenicol, proton pump inhibitors, or H2 blockers

Doctors usually use a blood test to check vitamin B-12 status, but home urine tests are also available. A doctor can check vitamin B-12 as part of a standard blood test.

Although it is not necessary to fast before a B-12 test, a person may need to if the doctor is also using the test to look at other components in the blood.

It is important that individuals tell their doctor about any medications and supplements they are taking, as some can affect the results.

The results may be:

  • Low. Levels of vitamin B-12 are low if they are below 200 pg/mL. This result suggests a vitamin B-12 deficiency, pernicious anemia, or an overactive thyroid. People with low vitamin B-12 levels often experience neurological symptoms.
  • High. An abnormally high vitamin B-12 status is anything over 900 pg/mL. This result may suggest liver or kidney problems, diabetes, or certain forms of leukemia.

The result ranges vary from one laboratory to another, so it is important to discuss the results and their meaning with a doctor.

The doctor may also check the levels of methylmalonic acid (MMA) and other substances to evaluate for vitamin B-12 deficiency. These lab values help detect a vitamin B-12 deficiency during the early stages.

Individuals with low vitamin B-12 levels often require regular injections of the vitamin. These shots are more effective than supplements at raising vitamin B-12 levels, especially when people have medical conditions that may make it more difficult to absorb supplements.

For some people, high doses of vitamin B-12 supplements may improve B-12 status. Supplements are available in capsule or liquid form from pharmacies, supermarkets, health stores, and online. It may also be helpful to eat more foods that are rich in vitamin B-12.

There is no upper limit for vitamin B-12 intake because consuming high levels does not cause problems. However, having naturally high levels of vitamin B-12 in the body may be a cause for concern, as it suggests a severe underlying condition. Doctors will aim to treat the underlying medical condition, rather than the elevated levels of vitamin B-12.

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Eggs are rich in vitamin B-12.
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Eggs are rich in vitamin B-12.

Although absorption difficulties and other medical issues often cause low vitamin B-12 levels, some people may be deficient because they do not get enough vitamin B-12 from their diet. This is especially true for vegans and long-term vegetarians.

Foods rich in vitamin B-12 include:

  • fish and seafood
  • meat
  • eggs
  • dairy products
  • fortified plant-based dairy alternatives
  • fortified breakfast cereals
  • fortified nutritional yeast

Vitamin supplements can make up for a shortfall in the diet, especially for vegans and strict vegetarians. As it can be easier for their body to absorb supplements than naturally occurring vitamin B-12, older adults should aim to meet their vitamin B-12 needs through fortified foods and vitamin supplements.

Recommended dietary allowances of vitamin B-12

Adults and adolescents over 14 years of age require 2.4 micrograms (mcg) of vitamin B-12 daily. This increases to 2.6 mcg during pregnancy, and 2.8 mcg when breast-feeding.

Vitamin B-12 is an essential nutrient that plays a vital role in overall health. A vitamin B-12 level test determines a person’s vitamin B-12 status. A doctor may recommend this test to people who have symptoms of a deficiency or who have a higher risk of low vitamin B-12 in the body.

People can avoid vitamin B-12 deficiency by eating a balanced diet and including several sources of vitamin B-12 daily or taking supplements. If they have issues absorbing vitamin B-12 from food sources, oral supplements or injections of the vitamin can help to prevent symptoms and complications.