Vitamin B12
(Specimen Container)
SST (Tiger Top)/ Lithium Heparin/ Sodium Heparin
(Transport Temperature)
| Temperature | Period |
|---|---|
| Room temperature | 72 hours |
| Refrigerated | 7 days |
| Frozen | If delayed longer than the max RT or 2-8°C, store frozen |
Vitamin B12 (B12), a member of the corrin family, is a cofactor for the conversion of methylmalonyl Coenzyme-A (CoA) to succinoyl CoA. In addition, B12 is a cofactor in the synthesis of methionine from homocysteine, is implicated in the formation of myelin, and, along with folate, is required for DNA synthesis.
B12 is absorbed from food after binding to a protein called intrinsic factor which is produced by the stomach. Causes of vitamin B12 deficiency can be divided into three classes: nutritional deficiency, malabsorption syndromes, and other gastrointestinal causes. B12 deficiency can cause megaloblastic anemia (MA), nerve damage and degeneration of the spinal cord. Lack of B12, even mild deficiencies, damages the myelin sheath that surrounds and protects nerves, which may lead to peripheral neuropathy. The nerve damage caused by a lack of B12 may become permanently debilitating, if the underlying condition is not treated. People with intrinsic factor defects who do not get treatment eventually develop a MA called pernicious anemia (PA).
The relationship between B12 levels and MA is not always clear in that some patients with MA will have normal B12 levels; conversely, many individuals with B12 deficiency are not afflicted with MA. Despite these complications, however, in the presence of MA (e.g., elevated mean corpuscular volume (MCV)) there is usually serum B12 or folate deficiency.
The true prevalence of B12 deficiency in the general population is unknown but increases with age. In one study, fifteen percent of adults older than 65 years old had laboratory evidence of vitamin B12 deficiency.
A serum B12 level below the normal expected range may indicate that tissue B12 levels are becoming depleted. However, a B12 level in the low normal range does not ensure that B12 levels are adequate and symptomatic patients should be further evaluated with tests for holotranscobalamin, homocysteine and methylmalonic acid.
There are a number of conditions that are associated with low serum B12 levels, including iron deficiency, normal near-term pregnancy, vegetarianism, partial gastrectomy/ileal damage, celiac disease, use of oral contraception, parasitic competition, pancreatic deficiency, treated epilepsy, and advancing age. Disorders associated with elevated serum B12 levels include renal failure, liver disease, and myeloproliferative diseases.
200 – 835 pg/mL
