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A vitamin B-12 level test checks the amount of vitamin B-12 in the blood to gauge the body's overall vitamin B-12 stores.

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

Vitamin B12 can take two forms in the body: Active B12 (or ‘holotranscobalamin,’ as the medical professionals might call it!) and Inactive B12.

The active form of B12 can be used by the body, where the inactive form cannot. In other words, it’s the levels of active B12 we really need to be concerned with if we are worried about thyroid issues, fatigue or any other symptoms associated with a B12 deficiency.


Vitamin B12 (cobalamin) is necessary for haematopoiesis and normal neuronal function. In humans, it is obtained only from animal proteins and requires intrinsic factor (IF) for absorption. The body uses its vitamin B12 stores very economically, reabsorbing vitamin B12 from the ileum and returning it to the liver; very little is excreted.

Vitamin B12 deficiency may be due to lack of IF secretion by gastric mucosa (eg, gastrectomy, gastric atrophy) or intestinal malabsorption (eg, ileal resection, small intestinal diseases).

Vitamin B12 deficiency frequently causes macrocytic anaemia, glossitis, peripheral neuropathy, weakness, hyperreflexia, ataxia, loss of proprioception, poor coordination, and affective behavioural changes. These manifestations may occur in any combination; many patients have the neurologic defects without macrocytic anaemia.

Pernicious anaemia is a macrocytic anaemia caused by vitamin B12 deficiency that is due to a lack of IF secretion by gastric mucosa.

Serum methylmalonic acid and homocysteine levels are also elevated in vitamin B12 deficiency states.


No special preparation required.

However, you should notify us if the patient have received a vitamin B12 injection within the last 2 weeks. Patient results will not reflect deficiency or malabsorption after recent B12 injection. If patient has received an injection within the past 2 weeks, this test should not be ordered.


A vitamin B12 level less than 180 ng/L may cause megaloblastic anaemia and peripheral neuropathies.

Vitamin B12 levels less than 150 ng/L is considered evidence of vitamin B12 deficiency. Follow-up with a test for antibodies to intrinsic factor is recommended to identify this potential cause of vitamin B12 malabsorption. For specimens without antibodies and the patient is symptomatic, follow-up testing for vitamin B12 tissue deficiency may be indicated. Consider analysis of methylmalonic acid and/or homocysteine.

Patients with serum vitamin B12 levels between 150 and 400 ng/L are considered borderline and should be evaluated further by functional tests for vitamin B12 deficiency. Plasma homocysteine measurement is a good screening test where a normal level effectively excludes vitamin B12 and folate deficiency in an asymptomatic patient. However, the test is not specific and many situations can cause an increased level. In contrast, an increased serum MMA level is more specific for cellular-level B12 deficiency and is not increased by folate deficiency.

In patients being evaluated for vitamin B12 deficiency who have intrinsic factor blocking antibodies (IFBA), false elevations of vitamin B12 may occur due to IFBA interference, potentially obscuring a physiological deficiency of vitamin B12. If observed vitamin B12 concentrations are discordant with clinical presentation, measurement of methylmalonic acid (MMA) should be considered.


Patients taking vitamin B12 supplementation may have misleading results.

Many other conditions are known to cause an increase or decrease in the serum vitamin B12 concentration and should be considered in the interpretation of the assay results, including:

Increased serum vitamin B12

Decreased serum vitamin B12

Ingestion of vitamin C


Ingestion of oestrogens


Ingestion of vitamin A


Hepatocellular injury


Myeloproliferative disorder

Ethanol ingestion


Contraceptive hormones






Multiple myeloma

The evaluation of macrocytic anaemia requires measurement of both vitamin B12 and folate levels; ideally, they should be measured simultaneously.

Some patients exposed to animal antigens, either in the environment or as part of treatment or imaging procedure, may have circulating antianimal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results.


The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario. Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

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