Last edited 04/2020 and last reviewed 02/2022
- 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)