Vitamin B12

Keywords: B12, Vit B12, Cyanocobolamin

Specimen:

5-10 mL blood in plain tube.

Method:

Immunoassay.

Reference Interval:

Refer to laboratory. Generally 120-680 pmol/L.

Application:

Investigation of a patient with a high MCV +/- anaemia and/or morphological changes (Blood film) suggestive of megaloblastosis.

Although significant Vitamin B12 deficiency with a normal FBC has been described in patients with neurological manifestations, this is rare and careful examination of the Blood film has shown occasional macrocytes and neutrophil hypersegmentation.

Interpretation:

Low in Megaloblastic anaemia due to Vitamin B12 deficiency.

Borderline levels may be seen in patients with Folate deficiency.

B12 assays measure the total B12 concentration, and not the biologically available B12. Holotranscobalamin provides a measure of the biologically available active B12, and should be consider in symptomatic patients with borderline B12 levels. 

Reference:

Chanarin I. The Megaloblastic Anaemias. 3rd ed. 1990. Blackwell Scientific.

Bain BJBlood cells: a practical guide. 4th Ed. 2007. Oxford: Blackwell Publishing.

Curtis AD et al. Clin Lab Haematol. 1986; 8: 135-140.