Vitamin B12 Test

Most commonly, a deficiency of vitamin B12 is suspected when a CBC test shows reduced haemoglobin levels. However, there are many other conditions that suggest the need for a vitamin B12 test. Following are the symptoms for which a vitamin B12 test is carried out:

• Loss of sensation in hands or feet
• Dementia
• Shortness of breath
• Irregular heartbeats
• Mouth ulcers and sores on tongue
• Confusion
• Loss of memory
• Fatigue and pallor

In addition, there may be some pre-existing conditions that interfere with the absorption of vitamin B12, which may result in a deficiency. Pernicious anaemia is an autoimmune condition in which antibodies attack the intrinsic factor, thereby affecting the absorption of vitamin B12. In celiac disease, Crohn’s disease or diabetes, the absorption of vitamin B12 is reduced.

Some medications, such as metformin and proton pump inhibitors, may also interfere with the absorption of this vitamin. A history of a gastric surgery can be a cause of its malabsorption and deficiency of vitamin B12.

Furthermore, excess levels of vitamin B12 are often associated with neoplasms, haematological malignancies and liver or kidney diseases. 

A vitamin B12 test is a simple blood test. It can be done anytime, and there is no requirement to fast before the blood sample is withdrawn from the body, unless specified by the physician. One must inform the doctor about their current medication or any supplements he or she is taking. This is necessary as some drugs interfere with vitamin B12 absorption and hence may show decreased levels.

This test is performed by collecting a blood sample from the arm of the patient. An experienced technician collects the blood sample from the arm by inserting a needle into a vein. This sample is then collected in a sterile tube. Slight pain may be sometimes felt while inserting the needle. The sample is then subjected to further analytical techniques such as immunoassays, High-performance liquid chromatography or, in recent times, radioisotope techniques to get accurate results.

Similarly, a blood smear test is a microscopic test that investigates abnormalities in blood. Hypersegmented neutrophils, which occur due to deficiency of vitamin B12, can be detected by this test and thus confirm vitamin B12 deficiency. Results are obtained within 12 hours of the test.

Normal results: It is very challenging to define normal limits of vitamin B12 in serum because the levels are affected by several factors. A gold standard reference method is not available, but to achieve harmonisation, levels of vitamin B12 up to 300 picograms (pg)/mL can be considered as normal.

Abnormal results: A serum concentration of vitamin B12 that is less than 200 pg/mL can indicate its deficiency, whereas levels between 200 pg/mL and 300 pg/mL can be considered borderline deficiency cases. It is, however, necessary to support the test results with some additional investigation. Deficiency of vitamin B12 causes an elevation in methylmalonic acid (MMA) and homocysteine levels. Similarly, the estimation of folate levels is also advised to support vitamin B12 tests. Abnormally low levels of B12 vitamin  may indicate the following health conditions:

• Neuropathy
• Ataxia
• Pernicious anaemia
• Megaloblastic anaemia
• Muscle weakness
• Macular degeneration in elderly patients

Similarly, elevated levels of vitamin B12, greater than 600 pg/mL, can be an early sign for haematological disorders such as leukaemia. Hence, additional tests studies are suggested.

Vitamin B12 test is highly recommended if the symptoms mentioned above are persistent. A blood test along with other supportive tests can help in the accurate diagnosis of the underlying disease.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. This information is purely from an educational perspective and is in no way a substitute for medical advice from a qualified doctor.