Vitamin B12: normal range, high and low

In shortNormal values are 299–1054 pg/mL (219–773 pmol/L). Values below 299 pg/mL (219 pmol/L) are a possible sign of deficiency, which is then confirmed by checking methylmalonic acid in the blood.

Reference ranges

Group	Reference range
Adults	299–1054 pg/mL (219–773 pmol/L)
Possible deficiency	Below 299 pg/mL (219 pmol/L)

Normal value ranges vary slightly among different laboratories, and some laboratories use different measurements or test different samples. A low result is confirmed with a methylmalonic acid test.

Reference range vs optimal — not the same thing

Deficiency can occur inside the reference range: neurological symptoms are described below ~300 pmol/L (~400 pg/mL). With symptoms, many clinicians treat 300–400 pmol/L as the lower comfort bound.

Check your value

Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.

A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.

What this marker is

The vitamin B12 level test measures how much vitamin B12 is in the blood. B12 — cobalamin — gives the body energy and helps keep nerves and blood cells healthy. A low level can cause numbness or tingling in the arms and legs, weakness, and loss of balance, which is why the test is also recommended for certain nervous system symptoms, severe confusion (delirium), loss of cognitive function (dementia), and nerve abnormalities such as peripheral neuropathy.

The test is most often done when other blood tests suggest megaloblastic anemia. Pernicious anemia causes a form of it: the stomach makes less intrinsic factor — the substance the body needs to absorb vitamin B12 efficiently — and the resulting B12 deficiency disturbs red blood cell production.

Results are reported in picograms per milliliter (pg/mL); in picomoles per liter (pmol/L) in many countries. The typical normal range is 299–1054 pg/mL (219–773 pmol/L). Values below 299 pg/mL (219 pmol/L) are a possible sign of deficiency — people with this degree of deficiency are likely to have or develop symptoms — and the finding is confirmed by checking methylmalonic acid: a high level of it indicates a true B12 deficiency.

Preparation includes fasting: no food or drink for about 6 to 8 hours before the test. Several medicines can affect the result — colchicine, H2 receptor blocking agents, metformin, neomycin, para-aminosalicylic acid, phenytoin, and proton pump inhibitors — so the provider reviews the medication list and decides whether anything is paused; no medicine is stopped without that advice.

When it is high

Uncommon findingAn increased vitamin B12 level is uncommon — excess B12 is usually removed in the urine.

Liver diseaseConditions such as cirrhosis or hepatitis can increase the B12 level.

Myeloproliferative disordersBlood disorders such as polycythemia vera and chronic myelogenous leukemia can raise B12.

When it is low

Not enough B12 in the dietDietary deficiency is rare, except with a strict vegetarian diet — B12 is found mainly in animal products.

MalabsorptionDiseases that cause malabsorption — for example celiac disease and Crohn disease — prevent the intestine from taking up enough B12.

Lack of intrinsic factorWithout this stomach protein the intestine cannot absorb vitamin B12 efficiently — the mechanism behind pernicious anemia.

HyperthyroidismAbove-normal body heat production, for example with an overactive thyroid, increases B12 consumption.

PregnancyThe need for B12 rises, and the measured level can fall.

What can skew the result

These factors can shift the value without any disease — worth considering before a retest:

Food and drink within 6–8 hours before the testColchicine, H2 receptor blocking agents, metformin, neomycin, para-aminosalicylic acid, phenytoin, proton pump inhibitors

How to prepare

No food or drink for about 6 to 8 hours before the test. The provider should know about all medicines — colchicine, H2 receptor blockers, metformin, neomycin, para-aminosalicylic acid, phenytoin, and proton pump inhibitors can affect the result — and decides whether any of them are paused; nothing is stopped without that advice.

When a retest makes sense

A value below 299 pg/mL (219 pmol/L) is a possible sign of deficiency and is confirmed with a methylmalonic acid blood test — a high methylmalonic acid level indicates a true B12 deficiency. The provider then looks for the cause: diet, absorption, or intrinsic factor.

Who usually reviews this result

A result outside the reference range is usually reviewed by: your GP or primary care doctor; a hematologist if anemia is the concern. Bring your lab report and any previous results to the appointment.

Names used on lab reports

Your report may use any of these names:
B12CobalaminCobalamin testPernicious anemia - vitamin B12 level

Units and conversion

Measured in: pg/mL

pg/mL = pmol/L

pg/mL × 0.738 = pmol/L. Example: 500 pg/mL = 369 pmol/L. Results are rounded to 2 decimal places.

Several markers on your report?

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Frequently asked questions

Why is a second test needed after a low result?

A low B12 value is a possible sign of deficiency, not proof. The confirmation test measures methylmalonic acid: when B12 is truly lacking, methylmalonic acid rises, so a high level of it indicates a true deficiency.

Which medicines distort the result?

Colchicine, H2 receptor blocking agents, metformin, neomycin, para-aminosalicylic acid, phenytoin, and proton pump inhibitors can all affect the measurement. The provider decides whether any of them should be paused.

Who is at risk of B12 deficiency?

People on a strict vegetarian diet, people with malabsorption from celiac disease or Crohn disease, people whose stomach makes too little intrinsic factor (pernicious anemia), people with hyperthyroidism, and pregnant women.

Sources

Vitamin B Test: MedlinePlus Medical Test — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.
Vitamin B12 level: MedlinePlus Medical Encyclopedia — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.

Vitamin B12