What It Measures
A serum Vitamin B12 test measures the total amount of cobalamin circulating in the blood. This reflects your body's B12 stores and its ability to absorb this vitamin from food or supplements. It is often measured alongside methylmalonic acid (MMA) and homocysteine for a more complete picture of functional B12 status.
Vitamin B12 (cobalamin) is a water-soluble vitamin essential for DNA synthesis, red blood cell formation, and neurological function. It plays a critical role in methylation pathways, homocysteine metabolism, and myelin sheath maintenance, making it a key marker for neurological health, energy production, and cardiovascular risk assessment.
Current Value
What High Means
Elevated serum B12 levels (>1000 pg/mL) can occur with supplementation (especially injections or high-dose oral forms) and are usually benign. However, unexplained high B12 without supplementation may indicate liver disease (hepatitis, cirrhosis), myeloproliferative disorders (polycythemia vera, chronic myeloid leukemia), kidney failure, or certain cancers. High B12 can also result from the release of B12 from damaged hepatocytes.
Possible Symptoms
Generally asymptomatic when due to supplementation. Unexplained elevations may present with symptoms of the underlying condition (e.g., jaundice or abdominal pain with liver disease, fatigue and night sweats with myeloproliferative disorders).
What Low Means
Low Vitamin B12 (<400 pg/mL functional deficiency; <200 pg/mL clinical deficiency) indicates inadequate intake, malabsorption, or increased demand. Common causes include pernicious anemia (autoimmune destruction of intrinsic factor), atrophic gastritis, celiac disease, Crohn's disease, long-term use of metformin or proton pump inhibitors, strict vegetarian/vegan diets, and chronic alcohol use. Deficiency leads to megaloblastic anemia, peripheral neuropathy, cognitive decline, and potentially irreversible neurological damage if untreated.
Possible Symptoms
Fatigue and weakness, numbness and tingling in hands and feet (paresthesias), difficulty walking and balance problems, cognitive difficulties (brain fog, memory loss), glossitis (swollen/inflamed tongue), mood changes (depression, irritability), pale or jaundiced skin, shortness of breath, heart palpitations, vision disturbances, muscle weakness
Risk Factors
Pernicious anemia, megaloblastic anemia, peripheral neuropathy, cognitive decline and dementia, depression, cardiovascular disease (via elevated homocysteine), neural tube defects in pregnancy, subacute combined degeneration of the spinal cord, glossitis, infertility
Actionable Advice
Supplements
- •Methylcobalamin
- •Adenosylcobalamin
- •Hydroxocobalamin
- •Cyanocobalamin
- •B-Complex (with methylated B vitamins)
- •Folate (methylfolate)
- •Betaine (trimethylglycine)
Diet & Lifestyle
- •Consume B12-rich foods: organ meats, clams, sardines, salmon, beef, eggs, dairy
- •If vegan/vegetarian, supplement B12 daily (methylcobalamin or hydroxocobalamin preferred)
- •Address gut health — low stomach acid or gut inflammation impairs B12 absorption
- •Limit alcohol intake, which depletes B12 and impairs absorption
- •Discuss B12 monitoring with your doctor if taking metformin or proton pump inhibitors long-term
- •Consider sublingual or injectable B12 if oral supplementation doesn't raise levels (suggests absorption issues)
- •Test methylmalonic acid (MMA) and homocysteine for functional B12 status if serum B12 is borderline
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Related Biomarkers
Resources & Studies
All Readings
| Date | Value | Change |
|---|---|---|
| 2025-06-27 | 511 pg/mL | — |