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Reference range

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

  • 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.


  • NHS Gloucestershire Foundation Hospitals Trust. Vitamin B12 and Serum Folate (Accessed 25/4/2020)

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