Vitamin B12 deficiency laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Laboratory Findings
Deficiency is defined as serum BTemplate:Ssublevels less than 200 pg/mL (95-100% specific). Borderline BTemplate:Ssub levels are defined between 200 and 400 pg/mL.
Serum BTemplate:Ssub levels are often low in BTemplate:Ssub deficiency, but if other features of BTemplate:Ssub deficiency are present with normal BTemplate:Ssub then the diagnosis must not be discounted. One possible explanation for normal BTemplate:Ssub levels in BTemplate:Ssub deficiency is antibody interference in people with high titres of intrinsic factor antibody.[1] Some researchers propose that the current standard norms of vitamin B12 levels are too low. In Japan, the lowest acceptable level for vitamin B12 in blood has been raised from about 200 picograms/litre (pg/l) = 145 picomol/litre (pm/l) to 550 pg/l = 400 pm/l. [2]
Serum Homocysteine and Methylmalonic acid levels are considered more reliable indicators of B12 deficiency than the concentration of B12 in blood, see for example research at the St. Louis University.[3] The levels of these substances are high in BTemplate:Ssub deficiency and can be helpful if the diagnosis is unclear. Approximately 10% of patients with vitamin B12 levels between 200-400pg/l will have a vitamin B12 deficiency on the basis of elevated levels of homocysteine and methylmalonic acid.
Routine monitoring of methylmalonic acid levels in urine is an option for people who may not be getting enough dietary BTemplate:Ssub, as a rise in methylmalonic acid levels may be an early indication of deficiency.[4]
If nervous system damage is suspected, B12 analysis in cerebrospinal fluid can also be helpful, though such an invasive test would be applicable only after unrevealing blood testing.[5]
- Methylmalonic acid: elevated in B12 deficiency (98% sensitive)
- Homocysteine: elevated in B12 and folate deficiency
- Anti-IF Antibodies (AB): highly specific for PA, but sensitivity only 50-84%
- Anti-parietal cell ABs: less sensitive and much less specific
References
- ↑ Hamilton MS, Blackmore S, Lee A. (2006). "Possible cause of flase normal B-12 assays (letter)". Brit Med J. 333 (7569): 654&ndash, 5.
- ↑ Mitsuyama Y, Kogoh H. (1988). "Serum and cerebrospinal fluid vitamin B12 levels in demented patients with CH3-
B12 treatment". Japanese Journal of Psychiatry and Neurology. 42 (1): 65–71. line feed character in
|title=at position 80 (help) - ↑ "Test used to diagnose B12 deficiency may be inadequate". Retrieved 2007-12-04.
- ↑ Donaldson MS. Metabolic vitamin BTemplate:Ssub status on a mostly raw vegan diet with follow-up using tablets, nutritional yeast, or probiotic supplements. Ann Nutr Metab. 2000;44(5-6):229-34. PMID 11146329.
- ↑ Devalia V (2006). "Diagnosing vitamin B-12 deficiency on the basis of serum B-12 assay". Brit J Med. 333 (7564): 385–6. PMID 16916826.