Vitamin B12 Deficiency

Vitamin B12 Deficiency

Dietary vitamin B₁₂ is solely derived from animal sources. The recommended daily intake is 1 to 2 micrograms.

In This Section

Clinical Effects

Causes

Pernicious anaemia
Total gastrectomy
Crohn’s disease
Ileal resection and blind loops
Small bowel lymphoma
Coeliac disease
Dietary (vegan)

Clinical Effects

Glossitis
Peripheral neuropathy
Posterior column degeneration (sub-acute combined degeneration of the cord)
Neuropsychiatric symptoms

Diagnosis

There is a macrocytic megaloblastic anaemia. Mild neutropenia and thrombocytopenia may occur.
A low serum vitamin B₁₂ level supports the diagnosis of vitamin B₁₂ deficiency but is not diagnostic. This is partly because the lower range of normal for serum vitamin B₁₂ is not clearly defined, particularly in the elderly. In addition, serum vitamin B₁₂ level falls without any other evidence of deficiency in pregnancy and with the oral contraceptive. B₁₂ also falls in primary folate deficiency.
A serum B₁₂ level, in the lower half of the normal range and particularly in the elderly, does not exclude B₁₂deficiency.
In view of this, other markers of Vitamin B₁₂ deficiency have been investigated such as methylmalonic acid excretion.
If B₁₂ deficiency is suspected, testing for intrinsic factor (IF) antibodies, which are present in 50% of patients with pernicious anaemia, will establish that diagnosis.
If the Vitamin B₁₂ level is low, and if IF antibodies are not present, B₁₂ absorption studies (Schilling Test) can be done. In practice, this is only performed in younger patients, usually to establish that life-long Vitamin B₁₂ injections are required.
For a discussion of the difficulties of diagnosing vitamin B₁₂ deficiency see Solomon L, Blood 105 - p. 978, 2005.

Management

If vitamin B₁₂ deficiency is strongly suspected on clinical or haematological grounds, even if the vitamin B₁₂ level is not low, give a trial of vitamin B₁₂ by injection, or start regular B₁₂ injections.
Monitor any response.
Oral B₁₂ is suitable for vegans.
Give vitamin B₁₂ 1000 micrograms subcutaneously every 3 to 4 days for six doses as an initial treatment. For long-term treatment, this should be followed by 1000 micrograms every two months.


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Last Reviewed:	November 2019
Next Review:	November 2022
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Note: Only the electronic version is controlled. Once printed, this is no longer a controlled document. Disclaimer The Haematology Department Protocols and Guidelines (the Red Book) are intended as a guide for registered health professionals to communicate guidelines and share best practices with supporting health professionals within New Zealand district health boards. They are not intended to be provided to or used as a reference for patients or non-registered health professionals. All health professionals must exercise their own clinical judgement and use pertinent clinical data when treating patients. The authors and editors of this publication have checked with sources believed to be reliable in their effort to provide information that is complete and in accord with the standards accepted at the time of publication. However, in view of the possibility of human error or changes in medical science, neither the authors, editors, publisher, nor any other party who has been involved in preparing or publishing this work warrants that the information contained in it is accurate or complete in every respect. They therefore have no liability (whether in tort (including negligence) or otherwise) for any loss or damage arising out of any reliance on this information. This publication has been compiled by the staff and contractors of Canterbury District Health Board (CDHB) and as such CDHB has copyright for this book. Amendments must be authorised in accordance with the documented process. No release of part of, or all of, this publication to any other party or organisation is permissible without the prior approval of the designated document owner.
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Topic Code: 6359