Vitamin B12 (also referred to as cobalamin, cyanocobalamin) is a coenzyme required for various metabolic functions in the body, including fat metabolism, carbohydrate metabolism, and protein synthesis. It plays an additional critical roles in hematopoiesis and a major role synthesizing and maintaining myelin in the central and peripheral nervous system.
Vitamin B12 deficiency is an important cause of reversible neuropsychiatric symptoms and often overlooked.[2][3][4] Many case reports and series have reported psychosis,[5] hallucinations,[6][7] mood, irritability, dementia, catatonia,[8] delirium, hallucinations, and other neuropsychiatric symptoms in B12 deficiency.[9][10] The specific association between the role of B12 deficiency and neuropsychiatric symptoms is not well understood due to the lack of studies.
Laboratory Test | Rationale for Test | Cut Offs | Advantages | Disadvantages |
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Cobalamin | Decreases in vitamin B12 deficiency | • Normal lab ranges vary greatly between labs, ranging from 150 to 350 pmol/L (110-258 pg/mL) • In adults, BC Guidelines suggest that B12 levels > 150 pmol/L are sufficient and unlikely to indicate B12 deficiency • A minimum level of 400-475 pmol/L (300 to 350 pg/mL) is desirable in the elderly.[13] BC guidelines • The conversion is 1 pg/mL = 1.355 pmol/L[14] | • Easily accessible • Most affordable • Most commonly used test with the most literature about abnormal cut-offs | Sensitivity and specificity is unclear |
Holotranscobalamin | • Decreases with vitamin B12 deficiency • Newer test, clinical utility unclear | 20-50 pmol/L | High sensitivity | Specificity unclear |
Methymalonic acid (MMA) | Increases with vitamin B12 deficiency | Normal level <260-412 µmol/L (varies) | High sensitivity | Questionable specificity |
Total homocysteine (Hcy) | Increases with vitamin B12 deficiency | Normal level <14 µmol/L | High sensitivity | Low specificity influenced by lifestyle factors (smoking, alcohol consumption, coffee consumption) |
Oral | • Cyancobalamin 1000mcg PO daily • Ranges from 300 to 2000mcg have been commonly used with no evidence of toxicity |
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IM | • Cyancobalamin 1000 mcg for 5 to 10 days to saturate B12 stores • Then 1000 to 2000 mcg qmonthly until normalization of the hemoglobin and hematocrit • Then 1000 mcg monthly to maintain remission |