Clinical investigations from the RACP

Low vitamin B12: what does it mean and what should I do?

James P Isbister



A low vitamin B12 level is a common finding, and interpreting its significance can be difficult. A low level should never be ignored because deficiency may be responsible for occult haematological or neuropsychiatric disease.

Key Points

  • Low vitamin B12 levels do not always indicate deficiency, but they should be investigated.
  • Low vitamin B12 levels are common in elderly patients, but the clinical significance may be difficult to determine.
  • It is possible that vitamin B12 deficiency may be responsible for cases of minor cognitive impairment, as well as the more classic neurological manifestations.
  • There is concern that the widespread use of folic acid therapy and dietary supplementation may precipitate clinical disease in individuals with occult vitamin B12 deficiency
  • Vitamin B12 assay results should always be interpreted in relation to the clinical context.