Vitamin B12
Shows whether you have enough B12 for energy, clear thinking, healthy nerves and red blood cells.
TypeBlood test
HowStandard blood draw.
How oftenIf at risk or with symptoms; yearly if deficient or on metformin.
BeforePause B12 supplements for a few days if possible.
WhoPlant-based eaters, 60+, people on metformin or acid-reducing medicines, and after gut surgery.
Why B12 is easy to miss
B12 comes mainly from animal foods and needs a healthy stomach to absorb. Low levels build slowly - causing fatigue, brain fog, tingling or low mood that’s easily blamed on something else.
Who’s at risk
“Could this be me?”
Vegans and vegetarians, 60+, metformin or acid-blocker users, and people with gut conditions.
Common causes
Borderline results
“My level is low-normal.”
Blood B12 can look OK while cells are short. MMA gives a clearer answer.
Check MMA
Why it matters
“Is it serious?”
Long-term deficiency can cause nerve damage - but it’s easy to treat once found.
Treatable
Is it right for you?
Worth considering if…
- You eat little or no animal food.
- You’re 60+ or take metformin or acid-reducing medicine.
- You have tiredness, brain fog, tingling or numbness.
A better option if…
- Your B12 is borderline - add MMA to confirm.
How it’s measured
Serum B12
The standard first test.
Active B12 (holotranscobalamin)
The portion your cells can use - offered by some labs.
MMA
A functional check if B12 is borderline.
The full picture
What is it?
A test of vitamin B12 levels in your blood.
What type of test is it?
A blood biomarker.
What does it measure?
B12 concentration.
Why might someone consider it?
Deficiency is common, causes vague symptoms and is easy to fix.
Who is it most relevant for?
People at risk or with symptoms.
How is it performed?
A blood draw.
How often might it be considered?
If at risk, or yearly with ongoing risk.
What can the result help you understand?
Whether you may need supplements or injections.
What are its limitations?
Borderline values are unreliable on their own.
What should it be viewed with?
MMA, homocysteine, folate, CBC and medications.
Where to get it
Through your provider
The simplest route - often covered when there’s a clear reason.
Lab services
e.g. Quest Diagnostics, Labcorp.
Direct-to-consumer panels
e.g. Function Health, InsideTracker.
Names are examples only, not endorsements. Your provider can often order the same test - and help interpret it.
Connected to
Questions to ask your provider
- Could my symptoms be low B12?
- Should I also check MMA?
Ziva Health
One test is a snapshot. Ziva shows the whole story.
Ziva brings your lab results, wearables and daily readings together - and Isabella tells you what’s changing and what to ask your provider next.
Refer Ziva to my provider / care team
Is your provider not on Ziva yet? Send them a link in under a minute - once they join, they’ll see your Vitamin B12 result alongside your other trends and get alerts directly.
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Bring your Ziva 30-day report to your next appointment - your Vitamin B12 result and daily trends in one view, so the conversation starts with the full picture.
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Being listed doesn’t mean everyone needs this test. Educational only — not medical advice. Results should be interpreted with a qualified clinician. ← Back to Know What to Test