Vitamin B12 · low result
Low vitamin B12: symptoms, causes and what level is deficient
Short answer
Low vitamin B12 — below about 200 pg/mL, with 200–300 a gray zone that methylmalonic acid clarifies — develops slowly and usually from poor absorption rather than diet: autoimmune pernicious anemia, metformin, long-term acid-suppressing medicines, stomach or bowel surgery, atrophic gastritis in older adults, celiac or Crohn's disease. Vegans and vegetarians, heavy drinkers, and people who use nitrous oxide are the main dietary and toxic exceptions. It causes fatigue, tingling or numbness, unsteadiness, memory and mood changes, a sore tongue and eventually anemia with large red cells; the nerve damage can become permanent, which is why borderline values with symptoms are treated rather than watched.
Medically reviewed by Youmna DiStefano, MD · Last reviewed November 2026
When does this result need same-day care?
- New numbness, weakness, trouble walking, vision loss or confusion — same-day care; nerve damage from B12 deficiency is time-sensitive and can become permanent
- Severe anemia symptoms — chest pain, breathlessness at rest, fainting — emergency care
- Deficiency in pregnancy or in an infant — prompt care; the developing nervous system is most vulnerable
What is the normal range for Vitamin B12?
- age 18+: 200 – 1100 pg/mL
Common in vegetarians/vegans, older adults, and people on metformin or acid-suppressing medications. Can cause anemia and neurological symptoms.
Full reference table, citations and testing options: Vitamin B12 biomarker page.
What are the common causes of low Vitamin B12?
- Pernicious anemia — autoimmune destruction of the stomach cells that make intrinsic factor, the protein needed to absorb B12; the most common cause of severe deficiency
- Metformin — lowers B12 by 10–30% after years of use; guidelines recommend periodic checking
- Long-term proton-pump inhibitors and H2 blockers — stomach acid is needed to free B12 from food
- Stomach and bowel surgery — gastric bypass or sleeve, gastrectomy, removal of the terminal ileum; Crohn's disease affecting the ileum
- Atrophic gastritis and Helicobacter pylori infection — the usual cause after 60, when B12 bound to food cannot be released
- Celiac disease, pancreatic insufficiency, small-intestinal bacterial overgrowth, and (rarely) fish tapeworm
- Diet — vegan and vegetarian eating without supplements, very low intake in older adults, alcohol use disorder
- Nitrous oxide — recreational use ('whippets') or repeated anesthesia inactivates B12 and can cause rapid, severe nerve damage
- Higher needs in pregnancy and breastfeeding, and exclusively breastfed infants of deficient mothers
What symptoms go with low Vitamin B12?
- Fatigue, weakness, pale or slightly yellow skin, breathlessness and palpitations
- Numbness or tingling in the hands and feet, burning feet, trouble with balance and walking, especially in the dark
- Memory problems, low mood, irritability, confusion — reversible when treated early
- A sore, red, smooth tongue, mouth ulcers, altered taste
- Blurred vision, in long-standing deficiency
- In infants: poor feeding, irritability, developmental delay
What do clinicians usually check next?
- Methylmalonic acid (with or without homocysteine) when B12 is 150–400 pg/mL or when symptoms are present with a 'normal' result — a raised MMA confirms the cells are short of B12
- CBC with MCV and a smear — large red cells and hypersegmented neutrophils support deficiency, but about a third of people have a normal MCV, especially with coexisting iron deficiency
- Intrinsic factor antibodies (specific for pernicious anemia), with parietal cell antibodies and gastrin when the picture is unclear
- Folate, because the two deficiencies travel together and folate alone can correct the anemia while nerve damage continues
- Celiac antibodies, TSH, and a review of metformin, acid suppressants and any nitrous oxide exposure
- Treatment: high-dose oral B12 (1,000–2,000 mcg daily) works for most people, including many with malabsorption, because about 1% is absorbed passively; injections are used for neurological symptoms, pernicious anemia and when oral treatment fails — then recheck in 8–12 weeks
- In pernicious anemia, a discussion about periodic endoscopy, because the associated gastritis raises the risk of stomach cancer and carcinoid tumors
Follow-up tests available at TestWell: CBC with Differential Test ($17.99), Homocysteine Test ($27.99), TSH Test (Thyroid Stimulating Hormone) ($20.99), TSH with Reflex to Free T4 Test ($29.99), TSH + Free T4 Test ($27.99), Methylmalonic Acid Test (MMA) ($48.99).
How do you recheck Vitamin B12?
Prices are cash-pay; every order adds one $6 lab processing fee. Physician authorization is included; no insurance or referral needed.
| Test or panel | Type | Price | Fasting | Results |
|---|---|---|---|---|
| Vitamin Deficiency Test Panel (D, B12 & Folate) | Panel · 3 tests | $89.99 | No | 1–3 business days |
| Comprehensive B12 Deficiency Panel | Panel · 3 tests | $79.99 | Yes | 5–12 business days |
| Autoimmune Gastritis Panel | Panel · 4 tests | $199.99 | Yes | 3–5 business days |
| Vitamin B12 Test | Test | $19.99 | No | 2–4 business days |
Common questions
Is a B12 of 250 low?
It is 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 and usually treatment.
What causes low B12?
Mostly absorption problems: pernicious anemia, metformin, long-term acid suppressants, stomach or bowel surgery, and atrophic gastritis in older adults. Vegan and vegetarian diets without supplements, heavy alcohol use and nitrous oxide are the main non-absorption causes.
What are the symptoms of low B12?
Fatigue, pale skin and breathlessness from anemia; numbness, tingling and unsteadiness from nerve involvement; memory and mood changes; and a sore, smooth tongue. The nerve and cognitive symptoms can appear before any anemia and are the reason not to wait on a borderline result.
Does metformin cause B12 deficiency?
It lowers B12 absorption, and after several years 10–30% of people on it have a low level. The American Diabetes Association recommends periodic B12 testing on metformin, particularly with anemia or neuropathy, which is otherwise often blamed on the diabetes itself.
Are B12 pills as good as shots?
For most people, yes — 1,000–2,000 mcg daily by mouth raises levels as effectively as injections even when absorption is impaired, because a small fraction crosses the gut without intrinsic factor. Injections are preferred when there are neurological symptoms, in pernicious anemia at the start of treatment, or when pills have not worked.
How long does it take to fix low B12?
Blood levels rise within weeks of replacement and the anemia corrects in 6–8 weeks; nerve symptoms improve over three to six months and may not fully reverse if long-standing, which is why early detection matters. Most absorption-related causes need lifelong replacement.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.