Vitamin B-12

Order Code

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2840

Preferred Specimen

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A 2 mL serum sample is required. Allow the SST tube to clot in an upright position for at least 30 minutes, then centrifuge the sample within 2 hours of collection. Refrigerate the serum.
Note: Avoid collecting samples from patients receiving high doses of biotin (>5 mg/day) until at least 8 hours after their last biotin dose.

ContainerType

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Serum separator tube

Alternate Specimen Requirements

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A 2 mL serum sample from a plain red top tube is acceptable. Let the sample clot in an upright position for at least 60 minutes, then centrifuge the sample and transfer the serum to a plastic transport tube within 2 hours of collection. Be sure to label the tube clearly as serum from a plain red top tube. Refrigerate the serum.
Note: As with the preferred specimen, do not collect samples from patients receiving high doses of biotin (>5 mg/day) until at least 8 hours after the last biotin dose.

Minimum Volume

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Adult: 1 mL serum
Pediatric: 0.2 mL serum (does not allow for repeat or
additional testing).

Transport Temperature

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Refrigerated

Expected Turnaround Time

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1 day

Specimen Stability

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1 day room temperature; 4 days refrigerated; 56 days frozen

Methodology

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Roche COBAS Electrochemiluminescent Immunoassay (ECLIA)

Rejection Criteria

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• Hemolysis
  allow only one freeze/thaw cycle
  

Overview

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Vitamin B12 is a water-soluble essential nutrient that plays a critical role in providing methyl groups necessary for protein and DNA synthesis. It is especially important for the production of blood cells and for the normal function of the brain and nervous system. Vitamin B12 exists in various forms, all containing cobalt, collectively known as cobalamins.

The daily requirement for B12 varies based on age and pregnancy status, typically ranging from 0.4–2.8 mcg/day (NIH, 2011). Due to its significant storage in the liver, clinical B12 deficiencies usually do not manifest until 4-5 years after a sustained decrease in intake or absorption. Vitamin B12 deficiency is particularly common in the elderly, those on long-term proton pump inhibitors or metformin, and vegetarians who do not consume enough B12. Deficiency symptoms may include anemia, tingling sensations, and cognitive decline. Elevated levels of serum methylmalonic acid and homocysteine are often early indicators of B12 deficiency.

Clinical Significance

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• Screen for B₁₂ deficiency, especially in the presence of long-term (>2 years) proton-pump inhibitor, H₂-blocker, or metformin use
• Evaluate symptoms of weakness, peripheral neuropathy, loss of balance
• Evaluate change of mental status, especially in the elderly
• Evaluate hypersegmented neutrophils, especially with elevated MCV
• Assist in diagnosis of certain anemias (eg, pernicious anemia, megaloblastic anemia)
• Part of evaluation for malnutrition (eg, liver disease, alcoholism) or malabsorption (eg, inflammatory bowel disease, sprue, cystic fibrosis)
• Assess effectiveness of treatment with B₁₂ supplementation

Additional Information

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Vitamin B12, which humans cannot synthesize, is produced by bacteria in the form of hydroxocobalamin. It is primarily found in animal-based foods such as meat, fish, poultry, dairy products, and eggs. Plant-based foods typically do not contain B12 unless they are fortified, usually with cyanocobalamin, a synthetic form of the vitamin derived from bacterial hydroxocobalamin. Regardless of the source, vitamin B12 is protein-bound and must be released by stomach acid. It then binds to intrinsic factor before being absorbed into the bloodstream. When consumed as cyanocobalamin, B12 is converted to its active forms, methylcobalamin and adenosylcobalamin, with minimal cyanide residue remaining.

Interpretative Information

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B12 Levels (ng/L or pg/mL)
High	>900	• Unusual as B vitamins are water-soluble and excess is typically excreted renally• Clinically asymptomatic• Most common cause is excessive vitamin supplementation• Rarely may be associated with serious underlying medical issues such as myeloproliferative disorders, hepatocellular injury, renal failure
Normal	300-900
Borderline Low	150-300	• Rarely due to inadequate intake (although vegans at risk) • Typically due to decreased absorption (eg, drug effect: proton pump inhibitors; H2 blockers; metformin) or malabsorption (eg, pernicious anemia, gastric bypass surgery, pancreatic insufficiency, celiac disease) • <200 may be associated with significant neuropsychiatric abnormalities • <180 associated with megaloblastic anemia and/or peripheral neuropathies
Low	<150
Important to note that ranges may overlap between cobalamin-deficient and normal individuals

Limitations

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Normal B₁₂ levels do not rule out tissue deficiency of vitamin B₁₂. If clinical concern exists, an assays for serum methylmalonic acid and homocysteine are indicated to detect early cellular B₁₂ deficiency (Klee, 2000).

References

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Diagnostic Role

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Serum B₁₂ is primarily ordered to detect and diagnose a low B₁₂ level, which is associated with an increased risk of certain anemias (eg, pernicious anemia, megaloblastic anemia), mental status and behavioral abnormalities, and peripheral neuropathy. A B₁₂ level is most commonly ordered in conjunction with a folic acid level as high levels of folic acid may mask B₁₂ deficiency by correcting megaloblastic anemia, a common finding in B₁₂ deficiency. Normal folate levels, however, do not correct any underlying nervous system damage due low B₁₂ levels, which may become irreversible with time.

In the clinical situation where B₁₂ deficiency is suspected and serum levels are low, no confirmatory testing is indicated. In cases where clinical suspicion exists and the B₁₂ level is in the low-normal range (200-300 ng/L), serum methylmalonic acid (MMA) and homocysteine levels should be checked to evaluate for early cellular B₁₂ deficiency. Both MMA and homocysteine are elevated in the presence of B₁₂ deficiency, while homocysteine alone is elevated in folate deficiency.

Long term use (>2 years) of proton-pump inhibitors and, to a lesser degree, H₂-blocking medications have been associated with B₁₂ deficiency by causing impaired breakdown of vitamin B₁₂ from food, decreasing B₁₂ absorption (Lam 2013). Vitamin B₁₂ deficiency has also been estimated to be present in up to 30% of metformin users due to malabsorption of food cobalamin in the distal ileum (Long, 2012).ging the inner lining of arteries and promoting blood clots. (AHA, 2014) However, lowering homocysteine levels has not been shown to decrease the risk for atherosclerosis or thrombosis. (Varga, 2005) At present, there are no broadly endorsed recommendations for formal testing of homocysteine levels in cardiovascular evaluations; however, such testing may aid in risk assessment in selected patients where established risk factors (tobacco use, hyperlipidemia, hypertension, diabetes) are absent, yet there remains a strong personal or family history of cardiovascular disease.

Alias

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• B-12

Test Setup Days

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Monday through Friday PM shift

CPT

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82607 Limited Coverage Test For Medicare.
Advance Beneficiary Notice Of Non-Coverage (ABN) Required
If Diagnosis Is Not Covered.
Frequency Limit Test For Medicare.
Advance Beneficiary Notice Of Non-Coverage (ABN) Always
Required For Frequency.
LOINC: 2132-9

Reference Range

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200-950 PG/ML

UNIT CODE	UNIT CODE NAME	ANALYTE	GENDER	AGE	REFERENCE RANGE	Units of Measure
2840	VITAMIN B-12	B12	NOT SPECIFIED	ALL	200-950	PG/ML
2840	VITAMIN B-12	B12	MALE	ALL	200-950	PG/ML
2840	VITAMIN B-12	B12	FEMALE	ALL	200-950	PG/ML