Vitamin B12 Levels

WHO Definitions	Vitamin B12 cut-off
B12 adequacy	> 221 pmol/L
Low B12	148 -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

message

• 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