Vitamin B₁₂

Serum

1 mL

0.7 mL (Note: This volume does not allow for repeat testing.)

Gel-barrier tube (preferred) or red-top tube

Fasting specimen preferred; must draw before Schilling test, transfusions or B₁₂ therapy is started.

Detect B₁₂ deficiency as in pernicious anemia; diagnose folic acid deficiency; evaluate hypersegmentation of granulocyte nuclei; follow up MCV >100; diagnose macrocytic anemia; diagnose megaloblastic anemia; evaluate alcoholism, prenatal care; evaluate malabsorption, neurological disorders, or the elevation of B₁₂ as seen in liver cell damage or myeloid leukemia

As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or have received them for diagnostic purposes.¹ In rare cases, interference due to extremely high titers of antibodies to streptavidin and ruthenium can occur.¹ The test contains additives, which minimize these effects.

Electrochemiluminescence immunoassay (ECLIA)

232−1245 pg/mL

Vitamin B₁₂, or cyanocobalamin, is a complex corrinoid compound containing four pyrrole rings that surround a single cobalt atom.² Humans obtain vitamin B₁₂ exclusively from animal dietary sources, such as meat, eggs, and milk. Vitamin B₁₂ requires intrinsic factor, a protein secreted by the parietal cells in the gastric mucosa, for absorption. Vitamin B₁₂ and intrinsic factor form a complex that attaches to receptors in the ileal mucosa, where proteins known as transcobalamins transport the vitamin B₁₂ from the mucosal cells to the blood and tissue.^3,4 Most vitamin B₁₂ is stored in the liver as well as in the bone marrow and other tissues.

Vitamin B₁₂ and folate are critical to normal DNA synthesis, which in turn affects erythrocyte maturation.^3,5,6 Vitamin B₁₂ is also necessary for myelin sheath formation and maintenance.⁷ The body uses its B₁₂ stores very economically, reabsorbing vitamin B₁₂ from the ileum and returning it to the liver so that very little is excreted.^4,8

Clinical and laboratory findings for B₁₂ deficiency include neurological abnormalities, decreased serum B₁₂ levels, and increased excretion of methylmalonic acid.^4,8,9 The impaired synthesis associated with vitamin B₁₂ deficiency causes macrocytic anemias. These anemias are characterized by abnormal maturation of erythrocyte precursors in the bone marrow, which results in the presence of megaloblasts and in decreased erythrocyte survival.^3,10

Pernicious anemia is a macrocytic anemia caused by vitamin B₁₂ deficiency that is due to lack of intrinsic factor.^5,6 Low vitamin B₁₂ intake, gastrectomy, diseases of the small intestine, malabsorption, and transcobalamin deficiency can also cause vitamin B₁₂ deficiency.³

Pregnant women need increased amounts of folate for proper fetal development.¹¹ If a woman has a folate deficiency prior to pregnancy, it will be intensified during gestation and may lead to premature birth and neural tube birth defects, such as spina bifida, in the child.¹¹