Vitamin B12 and Serum Folate

Department of Haematology


  • Vitamin B12 and serum folate are no longer performed on elderly patients in the acute setting unless there is a specific indication e.g. macrocytosis +/- anaemia, (pan)cytopenia, or blood film report comment.
  • This test will not be repeated if it has been carried out within the last 3 months.
  • This test can be added on to a patient request if the laboratory has an appropriate sample that is less than 3 days old.
  • Grossly haemolysed, lipaemic or icteric samples may give erroneous results and will not be processed
  • See also: Ferritin Assay; Intrinsic Factor Antibodies
  • Tests performed at CGH

Sample Requirements

5ml Gold-top SST tube or 3.5ml Rust-top gel tube (Trust users only)

Clotted sample

Wherever possible, please send separate samples for haematinics and biochemistry.

Turnaround Times

3 working days from request

Reference Ranges

Analyte Range Units
Vitamin B12 180 - 1000 pg/ml
Folate >4.0 ng/ml


Please note:

  • The 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.
  • The usual fall in Serum B12 concentration in pregnancy does not reflect B12 deficiency at the biochemical level. In establishing true B12 deficiency in pregnancy, the serum homocysteine level (in the absence of folate deficiency) may be of value, as an elevated homocysteine level is only seen in pregnant women with haematological evidence of B12 deficiency.

Result Interpretation

Serum Folate

Serum folate falls rapidly with an inadequate diet despite sufficient body stores . It is however more reliably analysed than Red Cell folate and is therefore used to screen for folate deficiency.

The common causes of deficiency are inadequate diet, malabsorption, anti-folate drugs (especially anticonvulsants) and occasionally in association with any disease that causes increase cell turnover, e.g. exfoliation.

Vitamin B12

B12 Investigation and Treatment Algorithm

Interpretation is difficult. The following observations are offered.

  • 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.
  • Interpretation of early megaloblastic change in the marrow is difficult and cannot be reliably distinguished from myelodysplasia.

The following is advised:

Testing should be restricted to those with a suspected vitamin B12 deficiency (macrocytosis, anaemia, neurological deficit, glossitis or clinical condition known to cause B12 deficiency) and should not be used as a screening test.

When the B12 level is less than 150 pg/ml a presumptive diagnosis of B12 deficiency is made. Where the cause is not known, the laboratory will automatically check for intrinsic factor antibodies. If these are negative, a clinical decision has to be made as to whether further investigation is necessary for patient management. If the B12 is between 150 and 180 pg/ml, a therapeutic trial should be given. If there is a clinical response then a diagnosis of B12 deficiency is made and the appropriateness of further investigation as to cause should be determined.

If there is no response, it is likely that the patient is not B12 deficient and other causes of the clinical problem must be sought.

If further investigation is required, please contact a Consultant Haematologist.

Page last updated: 13/11/2015