Vitamin B12 Blood Test

The Vitamin B12 Blood Test measures the level of B12 (cobalamin) in your blood. B12 is essential for methylation, red blood cell formation, DNA synthesis, and healthy nerve function. In the methylation cycle, B12 partners with folate to convert homocysteine back to methionine. Low B12 can contribute to elevated homocysteine, anemia, fatigue, and neurologic symptoms. As part of the PlexusDx Methylation Panel, B12 testing is paired with Folate (B9) and Homocysteine to give a complete picture of your one-carbon metabolism and nutrient status.

Why Measure Vitamin B12?

Methylation health: B12 (as methylcobalamin) is a cofactor for methionine synthase, helping recycle homocysteine.
Neurologic support: Adequate B12 supports myelin integrity and healthy cognitive function.
Hematologic health: B12 is critical for red blood cell production; deficiency can cause megaloblastic anemia.
Energy & metabolism: Suboptimal B12 is associated with fatigue, weakness, and poor exercise tolerance.

What’s Included in the PlexusDx Methylation Panel

Vitamin B12 (Cobalamin) — cofactor for methylation and homocysteine remethylation.
Folate (Vitamin B9) — provides methyl groups and pairs with B12 in one-carbon metabolism.
Homocysteine — functional marker influenced by B-vitamin status and methylation efficiency.

How the PlexusDx Test Works

At-home collection: Simple finger-prick kit with prepaid return shipping.
Fast turnaround: Digital results typically within ~2 business days of lab receipt.
Direct access: Order online; HSA/FSA eligible.

Understanding Results (High-Level)

Reference ranges vary by laboratory and reporting units. Your report will include the range used by the testing lab. In general:

Within range: Suggests adequate B12 for hematologic and neurologic needs.
Low or borderline: May contribute to elevated homocysteine, anemia, fatigue, neuropathy, and cognitive changes. Consider clinical correlation and follow-up testing.
High: Commonly reflects supplementation; persistent high levels should be interpreted in clinical context (e.g., assess functional markers if symptoms persist).

What Can Influence Vitamin B12 Levels?

Dietary intake: B12 is found in animal-derived foods (fish, dairy, eggs, meat) and fortified products.
Absorption factors: Low stomach acid, intrinsic factor deficiency, or GI conditions (e.g., celiac, IBD) can reduce absorption.
Medications: Metformin, PPIs/H2 blockers, and certain other drugs may lower B12 over time.
Genetics: Variants in transport enzymes (e.g., TCN2) or folate cycle genes may influence functional B12 needs.
Lifestyle & health: Alcohol overuse, vegan/vegetarian diets without fortified foods or supplements, and aging can increase risk of insufficiency.

Ways to Support Healthy B12 Levels

Nutrition: Include B12-rich foods (salmon, sardines, eggs, dairy, lean meats) or fortified alternatives if plant-based.
Supplementation: Talk to your clinician about forms and dosing:
- Methylcobalamin — active form used in methylation.
- Hydroxocobalamin — longer-acting form often used clinically.
- Cyanocobalamin — stable, commonly used form.
Address root causes: Evaluate GI health, medications, and co-nutrients (folate, B6, riboflavin, choline, betaine).
Re-testing: Recheck per your clinician’s plan after dietary or supplement changes.

FAQs

Can B12 be “normal” but not functional?
It’s possible to have serum B12 in range yet still have symptoms. Your clinician may consider complementary markers (e.g., homocysteine as part of this panel) and your clinical picture.

I’m plant-based. How do I maintain B12?
Use fortified foods and consider supplementation. Regular screening helps ensure adequacy over time.