Diagnosis of Vitamin B12 Deficiency

Updated at: Jan 18, 2013
Diagnosis of Vitamin B12 Deficiency

As the symptoms of B12 deficiency are non-specific, diagnosis becomes difficult without proper testing. If your doctor suspects vitamin B12 deficiency, he or she may recommend testing of serum vitamin B12 levels, complete blood count (CBC) and per

Dr Poonam Sachdev
Blood DiseasesWritten by: Dr Poonam SachdevPublished at: Jun 19, 2012

Vitamin B12 deficiency is very common, and many people who have it may not realize that they are suffering from symptoms of vitamin B12 deficiency. B12 deficiency causes non-specific symptoms in most people, which make diagnosis very difficult without elaborate testing.

Vitamin B12 levels: Serum vitamin B12 level is considered to be a useful initial diagnostic test for B12 deficiency, as it is widely available and labs and doctors are familiar with the test. In most cases, vitamin B12 deficiency is diagnosed based on finding low serum vitamin B12 (generally, <200 picograms/mL) and clinical symptoms suggestive of vitamin B12 deficiency. Unfortunately, a neurological disease because of vitamin B12 deficiency may be irreversible. Hence early detection is considered to be critical in preventing permanent neurological damage.

Serum vitamin B12 level on testing is interpreted as follows:

  • Likely vitamin B12 deficiency: <148 picomols/L (<200 picograms/mL).
  • Possible vitamin B12 deficiency: 148 to 258 picomols/L (201 to 350 picograms/mL).
  • Unlikely vitamin B12 deficiency: >258 picomols/L (>350 picograms/mL).

If serum vitamin B12 level is less than 148 picomols/L (<200 picograms/mL) treatment is started. Clinical response and improvement in serum B12 levels during follow-up confirm vitamin B12 deficiency.

Markers of tissue deficiency: Currently there is no consensus among experts on what normal serum vitamin B12 level should be for optimal neurological and haematological function. Use of markers of tissue deficiency such as homocysteine, methylmalonic acid (MMA), and holotranscobalamin can help to diagnose vitamin B12 deficiency in earlier stages.

CBC with peripheral smear: A complete blood count (CBC) and peripheral smear can help to diagnose vitamin B12 deficiency. It can show evidence of deficiency such as macrocytosis (big size of red blood cell) and frank anaemia, leukopenia (low white blood cell count), or thrombocytopenia (low platelet count). If these changes are found, they suggest severe and prolonged vitamin B12 deficiency. However, if red blood cell size, haemoglobin, and haematocrit are normal, it does not rule out tissue vitamin B12 deficiency, as many patients with vitamin B12 deficiency may have normal haematological parameters.

Your doctor may consider testing for vitamin B12 if you are at risk of deficiency of this essential nutrient, or have symptoms suggestive of deficiency.

Some factors which increase the risk of vitamin B12 deficiency include:

  • Elderly people (advancing age increases the risk).
  • Chronic use of certain medicines (such as metformin, proton-pump inhibitors, and anticonvulsants).
  • Chronic GI illnesses (such as Crohn's disease and coeliac disease). These can cause malabsorption or inadequate absorption.
  • History of upper GI surgery, including gastrectomy, gastric bypass, or iliectomy.

Symptoms and signs suggestive of vitamin B12 deficiency:

  • Unexplained neurological problems (specifically, decreased vibration sense, difficulty in walking, tingling or numbness in fingers and toes).
  • Neuropsychiatric problems (such as poor memory, depression and dementia).
  • Angular cheilitis, glossitis of the tongue.
  • Macrocytic anaemia and thrombocytopenia.


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