Indications to measure vitamin B12 levels

Indications for measuring serum vitamin B12 level (1):

• Haematological (in increasing order of severity):
  • isolated red cell macrocytosis
  • macrocytic anaemia (esp. if MCV >110 fl)
  • pancytopenia (esp. if MCV >120 fl)
    
• Neurological or psychiatric:
  • peripheral neuropathy
  • cognitive change e.g. dementia
  • optic neuritis
    
• Gastrointestinal:
  • investigation of possible malabsorptive process
    
• Other (rare):
  • angular cheilosis
  • sore beefy red tongue

Haematological complications of vitamin B12 deficiency can present in the absence of neurological problems and vice versa.

Testing should be restricted to those with suspected vitamin B12 deficiency and should not be used as a screening test (2).

Reference:

• (1) Royal United Hospital Bath NHS Trust. Guidelines for the Investigation & Management of vitamin B12 deficiency (accessed 13/05/2022).
• (2) NHS Gloucestershire Foundation Hospitals Trust. Vitamin B12 and Serum Folate (accessed 13/05/2022).