1083. Cyanocobalamin (Vitamin B12)

Vitamin B12, or cobalamin, is a water-soluble vitamin that is essential for normal nervous system function and is involved in metabolic processes, including the metabolism of certain amino acids and fatty acids. Cyanocobalamin is one of the forms of vitamin B12 found in the human body. It is involved in DNA and RNA synthesis and supports normal function of the blood system. A significant decrease in cyanocobalamin levels is associated with the development of anemia.

The test is used to diagnose anemic conditions and diseases of the gastrointestinal tract. It should be performed together with tests for folate, iron, and holotranscobalamin levels.

Vitamin B12 is obtained from food or supplements because the body cannot produce it on its own. The main dietary sources of vitamin B12 are meat, fish, eggs, and dairy products. Plant-based foods generally do not contain B12 unless they have been fortified with it.

Proper absorption of the vitamin requires normal function of the stomach and small intestine. In the stomach, B12 binds to a special protein called intrinsic factor, after which it is absorbed in the terminal part of the small intestine. Therefore, deficiency can develop not only because of dietary factors but also because of impaired absorption.

After absorption, vitamin B12 enters the bloodstream and is stored mainly in the liver. The body's stores can last for a long time, so deficiency often develops gradually, and its manifestations may not appear immediately. There may be no noticeable symptoms in the early stages.

A B12 test measures the level of the vitamin in blood serum. For initial diagnosis, it is usually interpreted together with a complete blood count (CBC). A low B12 level may indicate vitamin B12 deficiency. If necessary, a physician may additionally order tests for methylmalonic acid and homocysteine. Elevated levels of these markers may indicate B12 deficiency at the cellular level. Depending on the purpose of the evaluation, tests for folate, iron metabolism parameters, including transferrin, and holotranscobalamin – the active fraction of vitamin B12 – may also be performed.

What is vitamin B12 responsible for?

Vitamin B12 is involved in DNA synthesis, blood cell formation, and maintenance of the protective sheath surrounding nerve fibers. It is essential for normal nervous system function and blood formation.

Prolonged B12 deficiency can lead to macrocytic anemia, in which red blood cells become enlarged and do not mature properly. Nervous system dysfunction may occur even in the absence of anemia.

Normal B12 levels in the blood

The term ‘normal B12 level in the blood’ refers to the reference range – the range against which the test result is compared. Its limits depend on the testing method and equipment used by the laboratory, so the values provided on the laboratory report should be used as the primary reference. The result is interpreted together with symptoms, overall health status, and other test findings.

Causes of low B12 levels

A low B12 level may be associated with:

• insufficient dietary intake, particularly in people following a vegan or strict vegetarian diet without B12-fortified foods or appropriate supplements;
• a condition in which the stomach stops producing a special protein called intrinsic factor, which is necessary for vitamin B12 absorption. This often occurs due to autoimmune gastritis, a condition in which the immune system mistakenly attacks and destroys the stomach cells that produce this protein;
• diseases of the stomach or intestines that impair nutrient absorption, including celiac disease or Crohn's disease;
• surgery involving the stomach or part of the small intestine, including bariatric surgery – procedures performed to treat obesity;
• long-term use of certain medications, such as metformin or medications that reduce stomach acid;
• inadequate nutrition or prolonged excessive alcohol consumption.

B12 deficiency can lead to anemia. When anemia is associated with autoimmune impairment of intrinsic factor production, it is called pernicious anemia. Vitamin B12 deficiency may cause fatigue, weakness, pallor, shortness of breath, dizziness, and a sore or reddened tongue. Numbness and tingling in the limbs, as well as problems with balance, memory, concentration, or mood, may also occur.

Causes of high B12 levels

An elevated B12 level is often associated with taking supplements or receiving vitamin B12 preparations. It may also occur in some diseases of the liver, kidneys, or blood and in other conditions. An elevated result by itself does not establish the cause and does not necessarily indicate an excess of vitamin B12 in the body. This finding, particularly when it is not related to the use of vitamins or supplements, requires consultation with a physician to determine whether further evaluation is needed.

A B12 test may be recommended when symptoms suggest possible vitamin deficiency, when abnormalities are found in a complete blood count, and for people at increased risk of inadequate B12 intake or impaired absorption.

When is B12 testing recommended?

The test may be considered:

• if a complete blood count shows anemia, enlarged red blood cells, or other abnormalities that may be associated with B12 deficiency;
• in cases of persistent fatigue, weakness, pallor, shortness of breath, or dizziness;
• in cases of unexplained numbness or tingling in the hands or feet, impaired balance, memory, or concentration;
• to monitor B12 levels during treatment for B12 deficiency, as recommended by a physician.

Who needs a vitamin B12 test?

The test may be recommended for:

• people who follow a vegan or strict vegetarian diet;
• people with celiac disease, Crohn's disease, atrophic gastritis, or other conditions that impair nutrient absorption;
• people who have undergone surgery involving the stomach or part of the small intestine (bariatric surgery);
• people who take metformin or medications that reduce stomach acid for a prolonged period;
• older adults, in whom B12 absorption may become impaired;
• pregnant and breastfeeding women because of their increased need for vitamin B12;
• people with prolonged inadequate nutrition or excessive alcohol consumption.

• Venous blood

In order to exclude factors that may affect the test results, we recommend to follow the preparation rules: