Assay

Vitamin B12

Key Words

B12, Cobalamin

Specimen Collection

Serum (brown) Plasma (orange)

Turnaround Time

24hrs

Test Indications

Serum total cobalamin (or vitamin B12) is the most commonly used test to measure vitamin B12 status; however, as there is no established ‘gold standard’ test that defines cobalamin deficiency, the most important factor when assessing the significance of vitamin B12 results (in the assessment of cobalamin status), is the clinical picture.

Investigation and management of B12 deficiency can be divided into two algorithms based on indications for assessment:

 ·         Strong suspicion with objective indications for testing

 ·         Investigation with no strong supportive evidence

Please refer to Guidelines for the diagnosis and treatment of cobalamin and folate disorders from the British Committee for Standards in Haematology (2014) - https://onlinelibrary.wiley.com/doi/full/10.1111/bjh.12959

In the presence of a discordant test result and strong clinical features of deficiency, treatment should not be delayed to avoid neurological impairment.

If there is strong objective evidence of B12 deficiency despite normal B12 levels then second line testing under specialist guidance is indicated. This guidance needs to be directed by a specialty appropriate to the patient: neurology, paediatrics, care of the elderly or haematology.

The measurement of vitamin B12 is not indicated in patients receiving B12 supplementation.

Elevated vitamin B12 levels may be seen in vitamin B12 supplementation, liver disease, kidney disease, myeloproliferative disorders, some solid neoplasms, including assay interference. The finding of an elevated vitamin B12 should be followed by consideration of its possible aetiology.

Laboratory handling and reporting:

The laboratory will store samples with a history of low B12 result in an adult patient (<196 pg/ml) for 7 days and suggest clinicians send an add-on request for gastric parietal cell antibody testing (if not previously done).

Please note, high titre intrinsic factor antibodies can interfere with the vitamin B12 (cobalamin) assay, leading to a falsely normal serum vitamin B12 level. If vitamin B12 levels are normal but deficiency is suspected, consider referral for gastric parietal cell antibody testing if not previously done.

For further information, please discuss with the duty Consultant Haematologist.

References:

Devalia, V., 2014. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. British Journal of Haematology, 166, 496-513

Wolffenbuttel B H R, et al., 2019. The many faces of Cobalamin (Vitamin B12) deficiency. Mayo Clin Proc Innov Qual Outcomes, 3(2): 200-214

Harrington DJ, 2017. Laboratory assessment of vitamin B12 status. J Clin Pathol, 70, 168-173

Hughes CF & McNulty H, 2018. Assessing biomarker status of vitamin B12 in the laboratory: no simple solution. Annals of Clinical Biochemistry, 55(2) 188-189

Interferences

No known common methodological interferences. Samples should be collected after a period of fasting.

Reference Range

< 1 month: 187 – 1866 pg/ml

1 - <12 months: 168 – 1675 pg/ml

1 - <12 years: 354 – 1599 pg/ml

12 - <19 years: 270 – 1132 pg/ml

Adult: 200 - 771 pg/mL

Analytical Error

4.5%

Reference Change Value

43.4%

Minimum retesting interval

Requests made within 28 days of a previous request on a patient are intervened