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Haematology
Vitamin B12 (cobalamin)
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A cofactor for DNA synthesis and for methylmalonyl-CoA metabolism, absorbed in the terminal ileum bound to intrinsic factor. Deficiency causes megaloblastic anaemia and a subacute combined neurological degeneration.
Reference interval
| Conventional (pg/mL) | SI (pmol/L) | |
|---|---|---|
| Adults | 200–900 pg/mL | 148–664 pmol/L |
Specimen: Serum (protect from light) · Conventional × 0.738 = SI
Causes of high values
Recent B12 supplementation or injections, liver disease, myeloproliferative disorders, renal failure; high values are rarely of clinical concern.
Causes of low values
Pernicious anaemia (autoimmune gastritis), gastrectomy, ileal disease or resection (Crohn disease), strict vegan diet, metformin and proton-pump inhibitor use, Diphyllobothrium infestation, nitrous oxide exposure.
Pre-analytical and method notes
Values of roughly 200 to 300 pg/mL (about 148 to 221 pmol/L) are borderline and the serum level can be normal despite tissue deficiency, so methylmalonic acid and homocysteine are used to confirm it. Deficiency thresholds differ between laboratories and guidelines, and biotin can interfere with some immunoassays. Reference intervals vary by laboratory, method and population; use the interval printed on the report.
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
- Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity (WHO/NMH/NHD/MNM/11.1). World Health Organization (2011) — Tier 1 (standards / international bodies)
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