Reference range

• serum B12 180-1000 pg/ml
  • reference ranges provided are for adults
  • reference ranges for infants and children are dependant on age. Results should be interpreted along with clinical features and other laboratory results
    
    
• B12 levels fall physiologically in pregnancy and this usually does not represent deficiency at a biochemical level
  • if the mother has otherwise unexplained anaemia (or has other clinical signs of B12 deficiency), consider a treatment trial of B12 replacement as suggested below (following local standard advice for non-pregnant individuals with low serum B12 values).

Interpretation is difficult. The following observations are offered (1).

• in clear cut deficiency, levels of B12 are nearly always <150 pg/ml and usually <100 pg/ml.
  • Pernicious anaemia is the cause of the majority of severe deficiencies in adults
    • around 50% of patients with pernicious anaemia have intrinsic factor antibodies while this antibody is rarely seen in normal controls
    • parietal cell antibodies are present in 90% of patients but are also seen in 1 - 2% of normal controls
• patients with B12 in the borderline range (150 - 180 pg/ml) may have either early B12 deficiency or be healthy "low normal".
• neurological disease or glossitis may occur without anaemia or macrocytosis and may be irreversible (1)
• interpretation of early megaloblastic change in the marrow is difficult and cannot be reliably distinguished from myelodysplasia (1)

Note that reference ranges may vary between laboratories.

Reference:

1. Devalia V, Hamilton MS, Molloy AM; British Committee for Standards in Haematology. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br J Haematol. 2014 Aug;166(4):496-513.