Vitamin B₁₂

• present in meat, fish, eggs, milk, butter (foods of animal origin)

• daily requirement ~ 1 µg (normal intake 10-15 µg)

• body stores (liver) 2-4 years

• deficiency causes megaloblastic anaemia

Uptake

• combines with intrinsic factor (secreted from gastric parietal cells)

• absorbed in terminal ileum

Deficiency

Clinical Features

• Gradual onset of anaemia

• mild jaundiceglossitis

• angular cheilosis

• sterility

• reversible skin pigmentation

• subacute combined degeneration of the cord

• increased homocysteine

  • arterial / venous thrombosis

  • foetal neural tube defects

• may be asymptomatic

Laboratory findings

• Full blood count

  • Macrocytic anaemia

  • leucocytes moderately reduced

  • platelets moderatley reduced

• Blood film

  • hypersegmented neutrophils (>5 nuclear lobes)

• LFTs

  • bilirubin raised

  • lactate dehydrogenase raised

• Haematinics

  • B₁₂ normal or low

  • serum folate normal or raised

  • red cell folate normal or low

• Bone marrow

  • hypercellular

  • increased proprtion of early cells

  • megaloblastic erythropoeisis

  • giant metamyelocytes

• Others

  • raised serum methylmalonic acid (B₁₂ deficiency)

Causes of deficiency

• Inadequate diet

  • vegans

• Malabsorption

  • pernicious anaemia
  • bacterial colonisation of small intestine
  • stagnant loop syndromes
  • congenital / acquired ileum defects

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