NICE Clinical Knowledge Summaries
Anaemia – B12 and folate deficiency
Last revised in July 2020
- There is no gold standard test for measuring vitamin B12 deficiency, but the likelihood of deficiency can be determined by measuring serum cobalamin.
A serum cobalamin of less than 200 nanograms/L is sensitive enough to diagnose 97% of people with vitamin B12 deficiency.
- Clinical features of vitamin B12 deficiency can occur without anaemia and without low serum levels of vitamin B12.
- A normal MCV does not exclude the need for cobalamin testing, as neurological impairment occurs with a normal MCV in 25% of cases.
- Cobalamin levels are not easily correlated with clinical symptoms.
Pernicious anaemia (an autoimmune disorder which results in reduced production of IF) is the most common cause of severe vitamin B12 deficiency.
- People with pernicious anaemia may present with symptoms of associated disorders, for example, myxoedema, other thyroid disorders, vitiligo, stomach cancer, or Addison’s disease.
How should I manage people with confirmed vitamin B12 or folate deficiency?
- If cobalamin levels are low, check for serum anti-intrinsic factor antibodies.
- Also test people with strong clinical features of B12 deficiency, such as megaloblastic anaemia or subacute combined degeneration of the cord, despite a normal cobalamin level.
- Anti-intrinsic factor antibody is extremely specific for pernicious anaemia, with a high positive predictive value of 95%, but a low sensitivity of 40–60%. If anti-intrinsic factor antibody is present, pernicious anaemia is very likely, but its absence does not rule out a diagnosis of pernicious anaemia
How should I treat a person with vitamin B12 deficiency anaemia?
For people with neurological involvement
Seek urgent specialist advice from a haematologist.
Ideally, management should be guided by a specialist, but if specialist advice is not immediately available, consider the following:
Initially administer hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further improvement, then administer hydroxocobalamin 1 mg intramuscularly every 2 months.
For people with no neurological involvement
Initially administer hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks.
The maintenance dose :
Not thought to be diet related — administer hydroxocobalamin 1 mg intramuscularly every 2–3 months for life.