---
title: "Vitamin B12 test: what it measures, normal levels, and how B12 deficiency is confirmed"
type: biomarker
url: "https://www.test-well.com/biomarkers/vitamin-b12"
also_known_as:
  - b12
  - vitamin b12
  - cobalamin
category: Vitamins & Nutrients
units:
  - pg/mL
order_price_usd: 25.99
order_item: Vitamin B12
order_url: "https://www.test-well.com/tests/vitamin-b12"
reviewed_at: 2026-09-17
---

# Vitamin B12 test: what it measures, normal levels, and how B12 deficiency is confirmed

> Vitamin B12 is measured with a standard blood draw; no fasting is needed. A typical reference range is 200 – 1100 pg/mL. At TestWell it's $25.99 all-in as Vitamin B12, results in 2–4 business days, drawn at Quest or Labcorp. An out-of-range result is a prompt to look closer, not a diagnosis.

A vitamin B12 test measures the cobalamin circulating in your blood. Below about 200 pg/mL is deficient and above roughly 300 pg/mL is usually adequate, but the zone between is unreliable, and up to a quarter of people with a true deficiency have a 'normal' serum B12 — which is why methylmalonic acid (MMA) is added when the result is borderline or symptoms point to deficiency. No fasting is required.

Also known as: b12, vitamin b12, cobalamin.

## Key facts

| Fact | Value |
| --- | --- |
| Units | pg/mL |
| Sample | Blood draw |
| Fasting | Not required |
| Results | 2–4 business days |
| Price | $25.99 |
| Labs | Quest or Labcorp · BioReference in NY/NJ |

## What does a vitamin B12 test measure?

Vitamin B12 (cobalamin) is needed to make DNA, to form red blood cells and to maintain the myelin insulation around nerves. The body cannot make it; it comes from animal foods — meat, fish, eggs, dairy — and from fortified foods and supplements. Absorbing it is unusually complicated: stomach acid frees B12 from food, a stomach protein called intrinsic factor binds it, and the complex is absorbed only in the last part of the small intestine. A problem at any step leads to deficiency even with a good diet.

The standard serum B12 test measures the total cobalamin in blood, in picograms per milliliter (pg/mL; multiply by 0.738 for pmol/L). Most of that total is bound to a carrier protein (haptocorrin) that cells cannot use; only the fraction bound to transcobalamin — 'active B12' or holotranscobalamin — is available to tissues. Total B12 is still the usual first test because it is inexpensive and widely available, but its limitations explain why a second, functional test is often needed.

The functional tests are methylmalonic acid (MMA) and homocysteine. Both build up in blood when cells lack usable B12, so a raised MMA with a low-normal B12 confirms deficiency at the tissue level. MMA is the more specific of the two; homocysteine also rises with low folate, kidney disease and other conditions.

## Who should get a vitamin B12 test?

B12 is tested for two kinds of reasons: symptoms and risk. The symptoms include fatigue and shortness of breath from anemia, but also — and sometimes without any anemia — numbness or tingling in the hands and feet, unsteady walking, memory or concentration problems, low mood, a sore red tongue, and vision changes. Neurological symptoms are the reason not to delay testing; they can become permanent if deficiency goes unrecognized for long.

The risk groups are those with reduced intake or impaired absorption: vegans and vegetarians, especially during pregnancy and breastfeeding; adults over 60, in whom stomach acid production commonly declines; people taking metformin or long-term acid-suppressing drugs (proton-pump inhibitors, H2 blockers); anyone who has had bariatric surgery or removal of part of the stomach or terminal ileum; people with Crohn's disease, celiac disease, chronic pancreatitis or small-bowel bacterial overgrowth; those with autoimmune conditions such as type 1 diabetes or autoimmune thyroid disease, which travel with pernicious anemia; and people who use nitrous oxide recreationally, which inactivates B12.

A complete blood count showing large red cells (a high MCV) or unexplained anemia is another common trigger, as is monitoring in anyone already being treated for deficiency.

## How to get a vitamin B12 test and prepare for it

The test is a routine blood draw. Fasting is not required by most labs, though a morning draw before breakfast is a reasonable default if it is bundled with tests that do need fasting. Two preparation points matter. If you have had a B12 injection or are taking a high-dose oral supplement, the serum level will be high and will not reflect your underlying status; tell the interpreting clinician, or test before starting supplements if you are trying to establish a baseline. And because many B12 immunoassays rely on biotin–streptavidin chemistry, high-dose biotin supplements can interfere; stop them for at least two days beforehand.

B12 is rarely ordered alone. Folate is checked at the same time because the two deficiencies look alike on a blood count and folate treatment can mask B12 deficiency while nerve damage continues. A complete blood count shows whether anemia or large red cells are present, and MMA is either added up front or reflexed when the B12 result lands in the gray zone. You can order B12 or a B12 deficiency panel online through TestWell; a physician reviews the order, you visit a Quest or Labcorp patient service center, and results appear in your portal within a few business days.

## What is the normal range for Vitamin B12?

| Population | Reference range |
| --- | --- |
| age 18+ | 200 – 1100 pg/mL |

Reference intervals differ slightly between labs; the range printed on your report is the one to interpret against. Ranges are usually set so 95% of healthy people fall inside them.

## Normal vitamin B12 levels and the gray zone

Most US laboratories report an adult reference range of roughly 200 to 1,100 pg/mL, which is the range TestWell's catalog uses. The bottom of that range, however, is not a clean cut-off. A serum B12 below about 200 pg/mL (148 pmol/L) is consistent with deficiency, and above roughly 300 pg/mL deficiency is unlikely in someone without symptoms — but the 200 to 300 pg/mL band is genuinely indeterminate, and the British Society for Haematology guideline advises confirming or excluding deficiency there with MMA or homocysteine, particularly when symptoms or risk factors are present.

The test's imperfect sensitivity means a normal result does not fully exclude deficiency in a person with typical neurological symptoms; in that situation a functional test is appropriate even when the B12 is above 300 pg/mL. There is no established 'too high' threshold for harm from B12 itself; unusually high levels without supplementation are discussed below.

| Serum B12 | Interpretation |
| --- | --- |
| below 200 pg/mL (148 pmol/L) | Consistent with deficiency; treat and look for the cause |
| 200–300 pg/mL (148–221 pmol/L) | Indeterminate — check methylmalonic acid (or homocysteine) |
| 300–1,100 pg/mL | Deficiency unlikely; consider MMA if neurological symptoms persist |
| above the reference range | Usually supplements or injections; without them, liver, kidney or blood disorders are considered |

_Thresholds follow the British Society for Haematology (2014) and the NIH Office of Dietary Supplements._

## Why a normal B12 result can still mean deficiency — and why a high one may not mean much

Total serum B12 counts the cobalamin bound to haptocorrin, which tissues cannot use. Someone with a high haptocorrin level and a low active fraction can therefore have a reassuring total and a real deficiency. Liver disease, kidney disease and some blood conditions raise haptocorrin. Pregnancy and oral contraceptives lower the total without necessarily lowering the active fraction, in the other direction. This is the case for measuring MMA (or, where available, active B12) whenever the clinical picture and the number disagree.

A B12 level above the reference range is most often explained by supplements, injections or fortified foods and is not considered harmful in itself. When it appears without any supplementation, clinicians consider liver disease, kidney disease and certain blood disorders, because those raise the carrier proteins that hold B12 in the blood. The high-B12 section below covers these causes and the follow-up tests.

## What causes low vitamin B12

The most common cause in adults is impaired absorption rather than a poor diet. Food-bound malabsorption from low stomach acid — with age, from long-term acid-suppressing medication, or after gastritis — comes first. Metformin reduces absorption in a dose-dependent way. Pernicious anemia, an autoimmune attack on the stomach cells that make intrinsic factor, is the classic severe cause and is more common than most people expect, especially in those with other autoimmune conditions. Surgery on the stomach or terminal ileum, Crohn's disease, celiac disease, pancreatic insufficiency and bacterial overgrowth or fish tapeworm infection account for most of the rest.

Dietary deficiency does occur in strict vegans without supplementation, in breastfed infants of deficient mothers and in people with very restricted diets. Nitrous oxide use is an increasingly recognized cause of rapid, severe neurological B12 deficiency in young adults. The low-B12 section below sets out the causes in order of frequency along with the symptoms and next steps.

## What happens after a low or borderline B12 result

A clearly low result is usually treated without waiting, and the search for a cause runs alongside: intrinsic factor antibodies (and sometimes parietal cell antibodies) for pernicious anemia, a medication review, celiac serology and, when the history points there, gastrointestinal evaluation. A borderline result is resolved with MMA — a raised MMA confirms deficiency, a normal MMA makes it unlikely. Folate is corrected at the same time if low.

How B12 is replaced — oral or by injection, and how often — depends on the cause and severity and is decided with a clinician; people with pernicious anemia or after ileal surgery generally need lifelong treatment. Anyone with numbness, tingling, balance problems or cognitive change should be seen promptly rather than waiting for a repeat test, because the neurological effects are the ones that can become permanent. Response is checked with a blood count within weeks and a repeat B12 or MMA after a few months.

## What does a high Vitamin B12 mean?

A high vitamin B12 is usually from supplements or injections and is harmless — excess is excreted. Without supplements, an unexplained high B12 can reflect liver disease, kidney disease, or certain blood disorders, because those release or fail to clear B12-binding proteins. It's a prompt to review supplements first and check liver and kidney function if none explain it.

### Common causes of high Vitamin B12

1. Oral B12 supplements, energy drinks, multivitamins, B12 injections
2. Liver disease (hepatitis, cirrhosis, fatty liver)
3. Kidney disease
4. Blood disorders including myeloproliferative conditions (uncommon)

### Symptoms that go with high Vitamin B12

- None from the B12 itself

### What clinicians usually check next

- Stop or note supplements and recheck in a few weeks if the level was unexpected
- Liver and kidney panels, CBC if no supplement explains it

Follow-up tests at TestWell: [CBC with Differential](https://www.test-well.com/tests/cbc-with-differential) ($21.99), [CBC (Complete Blood Count)](https://www.test-well.com/tests/cbc) ($21.99).

**Can too much B12 hurt me?** Oral B12 has no established toxic level; the body excretes what it doesn't use. An unexplained high level without supplements is what deserves follow-up, not the supplement-driven kind.

## What does a low Vitamin B12 mean?

Low vitamin B12 causes fatigue, tingling, memory problems and eventually anemia, and it develops slowly — often from poor absorption rather than diet. Autoimmune pernicious anemia, metformin, long-term acid suppressants, gastric surgery, celiac disease and vegan diets are the common causes. Borderline results (roughly 200–300 pg/mL) can be functionally low; methylmalonic acid clarifies.

### Common causes of low Vitamin B12

1. Pernicious anemia (autoimmune loss of intrinsic factor)
2. Metformin, proton-pump inhibitors and H2 blockers with long-term use
3. Gastric bypass or other stomach surgery; atrophic gastritis in older adults
4. Celiac disease, Crohn's, small-bowel overgrowth
5. Vegan or strict vegetarian diet without supplementation
6. Nitrous oxide exposure

### Symptoms that go with low Vitamin B12

- Fatigue, weakness, pale skin
- Numbness or tingling in hands and feet, unsteady walking
- Memory problems, low mood, irritability
- Sore tongue, mouth ulcers

### What clinicians usually check next

- Methylmalonic acid (and sometimes homocysteine) for borderline values
- CBC with MCV — macrocytosis supports deficiency
- Intrinsic factor antibodies when pernicious anemia is suspected
- Folate, since the two deficiencies travel together

Follow-up tests at TestWell: [CBC with Differential](https://www.test-well.com/tests/cbc-with-differential) ($21.99), [CBC (Complete Blood Count)](https://www.test-well.com/tests/cbc) ($21.99), [Homocysteine](https://www.test-well.com/tests/homocysteine) ($27.99), [Methylmalonic Acid (MMA)](https://www.test-well.com/tests/methylmalonic-acid) ($49.99), [Folate (Vitamin B9)](https://www.test-well.com/tests/folate) ($32.99).

**Is a B12 of 250 low?** It's in the gray zone. Some people at that level have a true functional deficiency, which methylmalonic acid can reveal. Symptoms count — tingling or memory changes at 250 warrant follow-up.

**How long does it take to fix low B12?** Blood levels rise within weeks of replacement; nerve symptoms can take months to improve and may not fully reverse if long-standing, which is why early detection matters.

## How do you get tested for Vitamin B12?

| Order | Type | Price | Includes |
| --- | --- | --- | --- |
| [Vitamin B12](https://www.test-well.com/tests/vitamin-b12) | Single test | $25.99 | This marker |
| [Baseline Anemia Panel](https://www.test-well.com/tests/anemia-panel) | Panel | $74.99 | 5 tests |
| [Comprehensive B12 Deficiency Panel](https://www.test-well.com/tests/b12-deficiency-panel) | Panel | $79.99 | 3 tests |
| [Basic Vitamin Deficiency Panel](https://www.test-well.com/tests/vitamin-deficiency-panel) | Panel | $89.99 | 3 tests |
| [Chronic Fatigue Panel](https://www.test-well.com/tests/chronic-fatigue-panel) | Panel | $169.99 | 9 tests |

## Quest vs Labcorp vs BioReference

| Lab | Available | Price | Notes |
| --- | --- | --- | --- |
| Quest Diagnostics | Yes | $25.99 | Choose Quest at checkout; walk-in patient service centers in every state TestWell serves outside NY and NJ. |
| Labcorp | Yes | $26.99 | Choose Labcorp at checkout; walk-in patient service centers in every state TestWell serves outside NY and NJ. |
| BioReference (NY & NJ) | Yes | $24.99 | New York and New Jersey orders route here automatically — state rules keep Quest and Labcorp from accepting self-ordered draws. |

## Common questions about Vitamin B12

### What is a normal vitamin B12 level?

Most labs report about 200–1,100 pg/mL as normal. Below 200 pg/mL is consistent with deficiency; 200–300 pg/mL is a gray zone where methylmalonic acid is used to decide; above 300 pg/mL deficiency is unlikely unless you have typical neurological symptoms.

### Can my B12 be normal and I still be deficient?

Yes. Total serum B12 includes cobalamin bound to a carrier that cells cannot use, and its sensitivity is imperfect — a meaningful share of people with true deficiency test in the normal range. A raised methylmalonic acid confirms deficiency at the tissue level regardless of the serum number.

### Do I need to fast for a B12 test?

Most labs do not require fasting. Stop high-dose biotin for at least two days because it can interfere with the assay, and mention any recent B12 injection or high-dose supplement, which raises the level and hides your baseline.

### What is the difference between a B12 test and an MMA test?

Serum B12 measures how much cobalamin is in your blood; methylmalonic acid measures whether your cells have enough usable B12, because MMA accumulates when they do not. MMA is the confirmatory test when B12 is borderline or symptoms do not match the number.

### How long after stopping supplements should I wait before a B12 test?

There is no single answer — after a high-dose regimen or injections the level can stay elevated for months. If you need a true baseline, test before you start, or ask for methylmalonic acid, which reflects tissue status rather than recent intake.

### Does metformin cause B12 deficiency?

Long-term metformin reduces B12 absorption and lowers levels in a dose- and duration-dependent way. People on metformin, especially with anemia or neuropathy symptoms, are commonly tested periodically.

### Do I need a doctor's order to test my vitamin b12?

No. TestWell's licensed physician network reviews and approves your order — usually within minutes. You can place an order online without an in-person visit or a referral from your own doctor.

### How long does it take to get Vitamin B12 results?

Most Vitamin B12 results are available in 1–3 business days after your specimen arrives at the lab. You'll get an email the moment your results are ready, with everything viewable in your TestWell portal.

### How much does a Vitamin B12 test cost?

Our Vitamin B12 starts at $25.99. That's the all-in price — no copays, no insurance hoops, no surprise bills. HSA and FSA cards are accepted.

### Do I need to fast before my Vitamin B12 test?

Fasting is not required for the Vitamin B12 test. You can have your blood drawn any time of day.

### Which lab will process my Vitamin B12 test?

Your test will be processed by Quest Diagnostics, Labcorp, or BioReference depending on which is closest to you and which lab carries the test. All three are CLIA-certified and trusted by hospitals nationwide. You'll choose your lab during checkout from 4,000+ locations.

## Keep reading

- [Methylmalonic Acid (MMA) and B12 Deficiency: Why the Test Is Ordered and How to Read It](https://www.test-well.com/guides/methylmalonic-acid-b12-deficiency)
- [How to Read Your Blood Test Results](https://www.test-well.com/guides/how-to-read-your-blood-test-results)
- [Numbness and tingling: which blood tests?](https://www.test-well.com/symptoms/numbness-and-tingling)
- [Fatigue: which blood tests?](https://www.test-well.com/symptoms/fatigue)
- [Brain fog: which blood tests?](https://www.test-well.com/symptoms/brain-fog)
- [Dizziness and lightheadedness: which blood tests?](https://www.test-well.com/symptoms/dizziness)
- [Mood swings and irritability: which blood tests?](https://www.test-well.com/symptoms/mood-swings)
- [Shortness of breath: which blood tests?](https://www.test-well.com/symptoms/shortness-of-breath)
- [Before your test: Biotin supplements](https://www.test-well.com/prep/biotin)
- [Before your test: Common medications](https://www.test-well.com/prep/medications)

## Sources

- [AACC Lab Tests Online](https://www.testing.com/tests/vitamin-b12-and-folate/)
- [MedlinePlus (NIH) — Vitamin B Test](https://medlineplus.gov/lab-tests/vitamin-b-test/)
- [NIH Office of Dietary Supplements — Vitamin B12 Fact Sheet for Health Professionals](https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/)
- [British Society for Haematology — Guidelines for the diagnosis and treatment of cobalamin and folate disorders (2014)](https://doi.org/10.1111/bjh.12959)
- [FDA Safety Communication — Biotin may interfere with lab tests](https://www.fda.gov/medical-devices/safety-communications/update-fda-warns-biotin-may-interfere-lab-tests-fda-safety-communication)

## Related biomarkers

- [Vitamin D, 25-Hydroxy](https://www.test-well.com/biomarkers/vitamin-d-25-hydroxy)
- [Methylmalonic Acid](https://www.test-well.com/biomarkers/methylmalonic-acid)
- [Folate](https://www.test-well.com/biomarkers/folate)
- [Vitamin A (Retinol)](https://www.test-well.com/biomarkers/vitamin-a-retinol)
- [Vitamin B1 (Thiamine)](https://www.test-well.com/biomarkers/vitamin-b1-thiamine)
- [Vitamin B2 (Riboflavin)](https://www.test-well.com/biomarkers/vitamin-b2-riboflavin)

- [Reference range lookup tool](https://www.test-well.com/tools/reference-range-lookup)
- [Lab unit converter](https://www.test-well.com/tools/lab-unit-converter)
- [All biomarkers](https://www.test-well.com/biomarkers)

---

Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-17. Review policy: https://www.test-well.com/reviewers/youmna-distefano-md

Canonical page: https://www.test-well.com/biomarkers/vitamin-b12
Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt

Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.