Diagnostic Use
The major fraction (>80%) of plasma vitamin B12 is bound to haptocorrin (transcobalamin 1), and its function is unknown. The remainder (< 20%) is bound to transcobalamin II (TCII) and it is this fraction that is biologically active (available for delivery to cells). Vitamin B12 bound to TC11 is called holotranscobalamin.
Reduced level in:
- Vitamin B12 deficiency
- Dietary insufficiency
- Compromised gastric acid (e.g. due to gastrectomy, PPIs, metformin, atrophic gastritis)
- Exocrine pancreatic insufficiency
- Intrinsic factor deficiency
- Impaired absorption in the intestine (e.g. due to Coeliac and Chron’s disease)
- Reduction in active forms of B12 (e.g. due to nitrous oxide, intracellular disorders of B12 metabolism)
- Other
- Pregnancy
- Patients on oral contraceptives
- Transcobalamin deficiency
Raised level in:
- Patients on vitamin therapy
- Inflammatory conditions of the liver
- Myeloproliferative disorders
- Leukaemias
- Hypereosinophilic syndrome
Reference Intervals
170 – 800 pmol/L
(Borderline: 110 – 170 pmol/L)
Test Method
Principle: Electrochemiluminescence immunoassay - Competitive
Analyser: Roche Diagnostics Cobas e801
Reagents: Elecsys Vitamin B12 II
Limitations / Interference
Conditions which affect B12 binding proteins (such as malignancy, pregnancy, liver disease and autoimmune disorders) can cause this test to give a false impression of B12 activity.
Uncertainty of Measurement
10%