Vitamin B12 (Cobalamin)
Measures the vitamin B12 in your blood. Your nerves and red blood cells need B12, so this is the usual first check of your B12 status.
AI-drafted. Awaiting verificationAlso called B12, Vit B12, CblLOINC 2132-9
Check your result
Type your result to see where it falls.
Nothing you type here leaves your browser.
What it is
Vitamin B12 (cobalamin) comes from animal foods such as meat, fish, eggs and dairy, and from fortified foods and supplements. To absorb it, your stomach has to make a protein called intrinsic factor, and the end of your small intestine has to work well. Your liver stores several years' worth, so a shortage usually builds slowly. This test measures the total B12 in your blood. Most of it is attached to a protein that mainly holds it in the blood. A smaller part is attached to the carrier that delivers it to your cells.
Why it matters
B12 helps your body make red blood cells and DNA, and it keeps your nerves working. Too little can cause a type of anemia with large red blood cells, along with tingling or numbness in the hands and feet, balance problems, tiredness, and memory or mood changes. Nerve symptoms can appear even when blood counts look usual, and some nerve damage can become permanent if a shortage goes untreated, so a low result is worth following up. Many people with a slightly low result have no symptoms at all.
If it’s low
A low result means the amount of B12 in your blood is below your lab's range. It can be a sign that your body isn't getting or absorbing enough B12. Results near the lower edge are hard to read, though. Some people with a borderline result have enough B12 inside their cells, and some people with a result in the usual range are still short on B12 where it counts. That is why clinicians often follow a borderline result with a second test, such as methylmalonic acid (MMA), and look at your symptoms and blood counts too.
Common causes
- Eating little or no animal food, such as a vegan or mostly vegetarian diet without fortified foods or supplements
- Long-term use of certain medicines, including metformin and acid-reducing medicines (proton pump inhibitors and H2 blockers)
- Older age, when the stomach makes less acid and absorbs B12 from food less well
- Pregnancy, when the blood level normally dips, often without a true shortage
- Digestive conditions or surgery that affect absorption, such as Crohn's disease, celiac disease, stomach or small bowel surgery, and weight-loss surgery
- Pernicious anemia, an autoimmune condition in which the body can't make enough intrinsic factor
- Frequent nitrous oxide ("laughing gas") use
What can help
- Ask your clinician what is the most likely cause for you, because the right next step depends on it
- Include B12-rich foods such as fish, meat, eggs, dairy, and fortified cereals or plant milks
- If you eat a vegan diet, ask your clinician about fortified foods or a B12 supplement
- Ask whether a B12 supplement or B12 injections make sense for you, since people who can't absorb B12 well sometimes need a different route
- Ask whether any medicines you take long term could be playing a part, and don't stop any medicine on your own
If it’s high
A high B12 result most often comes from B12 supplements or recent B12 injections. Less often, a high level goes along with liver disease, kidney disease or certain blood disorders. A high result on its own doesn't point to a cause. Your clinician can read it alongside your supplements and your other results.
Common causes
- B12 supplements, including multivitamins, B-complex products and energy drinks or shots that contain B12
- Recent B12 injections
- Liver disease, including liver damage from heavy alcohol use
- Kidney disease
- Certain blood disorders in which blood cells are overproduced
What can help
- Tell your clinician about every supplement you take, including multivitamins and B-complex products
- Ask whether the result fits with your supplements and with your liver and kidney tests
- Ask whether a repeat test makes sense if you haven't been taking any B12
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 232–1,245 pg/mL. Source: Labcorp, MedlinePlus (National Library of Medicine).
- Adults (this one applies)232–1,245 pg/mL
Sources: Labcorp, MedlinePlus (National Library of Medicine)
BOND adult serum B12 cutoffs (2018)
- Severe deficiencybelow 75 pmol/L
- Deficient75 to under 150 pmol/L
- Depleted (some people are deficient; follow-up testing helps)150 to under 221 pmol/L
- Adequate221 and above pmol/L
Stepwise testing zones used in clinical algorithms
- Lowbelow 148 pmol/L
- Indeterminate (a second test such as MMA is usually added)148 to under 250 pmol/L
- Likely adequate250 and above pmol/L
If this applies to you
Vitamin B12 means a little more for some people. Open the one that fits you.
Had weight-loss surgery
Absorbing B12 needs stomach acid and a stomach protein called intrinsic factor, and gastric bypass and sleeve gastrectomy reduce both. Guidelines suggest regular B12 checks after these operations and after duodenal switch. The body's B12 stores can last about 2 years, so a shortage can build slowly.
Celiac disease or IBD
ACG notes that celiac disease can impair absorption of iron, fat-soluble vitamins and potentially B12 and folate. BSG lists B12 among the blood tests for people with IBD who are malnourished or at risk of it.
Hemochromatosis or iron overload
EASL advises checking vitamin B12 from time to time in people with hemochromatosis, especially those who need many phlebotomies.
Low iron or anemia
Low B12 can also cause anemia. BSG notes that it can hide the small-cell pattern of low iron and is one of the reasons iron treatment may not seem to work.
Age 65 or older
Older age, metformin and acid-reducing medicines called proton pump inhibitors are all linked to low B12. The ADA suggests checking B12 every year in older adults who have taken metformin for more than 4 years.
Prediabetes or diabetes
Metformin is linked to a higher chance of low B12 and to worse nerve symptoms. The ADA suggests periodic B12 testing for people taking metformin, and includes it in the yearly lab list after several years of use.
Vegan or vegetarian
B12 isn't found in plant foods, and the Academy notes that vegans without fortified foods or supplements can become deficient. A total B12 level is a weak guide on its own, a 2016 review found, so it is often read with MMA or active B12.
On a GLP-1 medicine
Eating much less can make it harder to get enough B12, which a 2025 joint advisory lists among nutrients of concern on these medicines. Many people with diabetes also take metformin, which the ADA links to low B12.
What can affect your result
- Diet: people who eat few or no animal foods are more likely to have low levels
- Pregnancy: levels usually fall by roughly a fifth and recover after delivery
- Age: B12 levels don't change much with age in healthy people, but low levels are more common in older adults
- Smoking is linked to somewhat lower levels
- Kidney disease, liver disease and heavy alcohol use can raise the result
- Supplements, multivitamins and injections taken before the draw raise the result
- Medicines such as metformin and acid reducers, when taken for a long time, can lower it
- Assay and lab: ranges and lower limits differ between labs and methods
- High-dose biotin supplements can interfere with some immunoassays used for B12. Labcorp advises stopping biotin at least 72 hours before the draw, so check with your clinician or lab first.
- Antibodies to intrinsic factor (seen in pernicious anemia) can interfere with some B12 assays and make a result unreliable.
- Recent B12 injections, supplements or multivitamins raise the result and can hide a shortage. Labcorp asks that blood be drawn before a transfusion, a Schilling test or B12 treatment begins.
- Some medicines are listed by MedlinePlus as able to affect the result, including metformin, acid-reducing medicines (H2 blockers and proton pump inhibitors), colchicine, neomycin, para-aminosalicylic acid and phenytoin.
Depends on the cause and the treatment. Once treatment starts, methylmalonic acid and homocysteine usually improve within about a week, and blood counts within about 8 weeks (AAFP 2017).
When to talk to a clinician
Talk with a clinician soon if your result is below about 200 pg/mL (148 pmol/L), or below your lab's range, particularly with numbness or tingling in your hands or feet, trouble with balance or walking, new memory or mood changes, a sore smooth tongue, or unusual tiredness or breathlessness. New or worsening nerve symptoms shouldn't wait for a routine visit. An unexplained very high result, when you aren't taking B12, is also worth raising with your clinician.
Questions you could ask
- Do my symptoms, my blood counts (such as MCV) and my B12 result fit together?
- Is there a reason for me to have my B12 checked regularly, for example because of my diet or medicines?
- Could my supplements explain this result?
- Should we check my liver and kidney tests or repeat this one?
- What might be causing my B12 to be low?
- Should we check methylmalonic acid or another test to see how my body is using B12?
Questions people ask
My B12 is in the usual range, but I have symptoms. Could it still be low?
It is possible. Total B12 in the blood is an imperfect measure. A small share of people with confirmed B12 deficiency (about 3 to 5 in 100) have a result above the common cutoff of about 200 pg/mL. Results in the lower part of the range are the hardest to interpret, so clinicians often add a second test such as methylmalonic acid. If you have symptoms, tell your clinician even if your B12 result looks fine.
Why do labs and websites list different ranges for B12?
Labs use different assays and different groups of people to set their ranges. For example, Labcorp lists 232–1245 pg/mL, while MedlinePlus gives 299–1054 pg/mL and notes that ranges vary. Many groups also use a cutoff of about 200 pg/mL (148 pmol/L) for a low result. Use the range printed on your own lab report.
How do I convert pg/mL to pmol/L?
Multiply pg/mL by 0.738 to get pmol/L, so 300 pg/mL is about 221 pmol/L. To go the other way, multiply pmol/L by 1.355. Some labs print ng/L, which is the same number as pg/mL.
Can a B12 supplement or multivitamin change my result?
Yes. Taking B12 in the days before a blood draw can raise the result and hide a shortage. Biotin supplements can also interfere with some B12 assays. Tell the person who orders your test about everything you take, and ask whether to pause any supplement first. Labcorp's guidance is to stop biotin at least 72 hours before the draw.
Does a low B12 mean I have pernicious anemia?
No. Pernicious anemia is one of several possible causes. Diet, long-term use of some medicines, age-related changes in the stomach, and digestive conditions can also lower B12. If the cause isn't clear, your clinician may order other tests, such as intrinsic factor antibodies.
Show the science and sources
Units
- 1 pg/mL = 1 pg/mL
- 1 pg/mL = 0.7378 pmol/L
Open the Vitamin B12 unit converter
Is a change real?
Vitamin B12 naturally varies about 6.7% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 21% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Biological variation of holotranscobalamin and cobalamin in healthy individuals (Brokner M et al.).
For clinicians and researchers
Serum or plasma total B12 is the sum of cobalamin bound to haptocorrin (about 70–80%, mainly a clearance and storage pool) and holotranscobalamin (about 20–30%, the fraction cells can take up). Clinical laboratories use automated competitive-binding immunoassays with intrinsic factor as the binder (Labcorp lists an electrochemiluminescence immunoassay). Earlier radioassays also picked up inactive cobalamin analogues, which using intrinsic factor as the binder avoids, and radioassays have largely been displaced by immunoassays. Total B12 lacks both sensitivity and specificity. Roughly 2.5–5% of patients with confirmed deficiency have values above the common 148 pmol/L (about 200 pg/mL) cutoff, and about 20% of people with low values show no clinical or metabolic sign of deficiency, so cutoffs remain contested. The BOND review (2018) lists adult serum B12 below 75 pmol/L as severe deficiency, 75 to below 150 as deficient, 150–221 as depleted and above 221 as adequate. Stepwise algorithms treat roughly 148–250 pmol/L as an indeterminate zone to be resolved with MMA (cutoffs of 271 or 376 nmol/L are used, and renal function should be checked), homocysteine or holotranscobalamin. Preanalytical and analytical caveats: serum B12 falls about 20% in pregnancy (25–30% between 20 and 30 weeks of gestation) through altered haptocorrin binding, with holotranscobalamin unchanged, and recovers by about 14 weeks postpartum; smokers have lower values; chronic kidney disease, liver disease, macrophage activation and anti-transcobalamin antibodies raise total B12; metformin lowers serum B12, although some evidence points to redistribution rather than true deficiency; intrinsic factor antibodies and biotin can interfere with immunoassays; lithium heparin can give gelatinous serum and raised values. B12 and folate are linked through the methyl-folate trap, so folic acid can correct the megaloblastic anemia of B12 deficiency while the neurologic damage continues. Reference intervals depend on assay and population, and infant ranges differ from adult ranges.
LOINC 2132-9 (primary), 14685-2, 35201-3. Specimen: serum-or-plasma.
Sources
- Vitamin B12 (test 001503), Labcorp
- Vitamin B12 level, MedlinePlus (National Library of Medicine) (2026)
- Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review, The Journal of Nutrition (2018)
- Biomarkers of vitamin B-12 status in NHANES: a roundtable summary, The American Journal of Clinical Nutrition (2011)
- Vitamin B12 Deficiency: Recognition and Management, American Family Physician (2017)
- Cyanocobalamin (molecular weight 1355.4 g/mol), PubChem (National Library of Medicine)
AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.