Vitamin B12 Levels

WHO DefinitionsVitamin B12 cut-off
B12 adequacy> 221 pmol/L
Low B12148 -221 pmol/L
B12 deficiency< 148 pmol/L
Pitfalls of Serum Vitamin B12
  • Neither sensitive, nor specific
  • Vitamin B12 levels mostly reflect the predominant but functionally inactive form of Vit B12 (bound to haptocorrin)
    • Haptocorrin: Binds 70 -90% of total B12
    • Transcobalamin: Binds 10 -30% of total B12
    • Does not reflect cellular vitamin B12 status
False negative (Normal level in deficient patient)
  • Myeloproliferative neoplasms and ALPS: Release haptocorrin
  • Exposure to nitrous oxide: Functional deficiency
  • Inherited Transcobalamin deficiency
  • Inborn errors of cobalamin metabolism
  • Oxidative stress in elderly
False positive (Low levels in non-deficient)
  • Megadoses of vitamin C (2 gm/day)
  • Inherited holocobalamin deficiency
  • Folate deficiency
  • Serum vitamin B12 has limited diagnostic value as a stand-alone marker
  • Low serum levels do not always represent deficiency
  • Severe functional deficiency has been documented in the presence of normal or even high levels

Next post : Other Bio Chemical Markers of Vitamin B12 Deficiency

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