What this test measures
A Vitamin B-12 test measures the concentration of cobalamin in your serum. B-12 is essential for healthy red blood cell formation, DNA synthesis, and the function of the nervous system. Humans cannot make B-12 — it must come from the diet (animal products) or supplements. The body stores B-12 in the liver, so deficiency develops slowly over months or years.
Most Indian labs report total serum B-12 in picograms per millilitre (pg/mL) using an immunoassay. If a value is borderline or symptoms are present despite "normal" B-12, doctors sometimes order more sensitive markers: methylmalonic acid (MMA), homocysteine, or active B-12 (holotranscobalamin).
Why it matters
India has one of the highest prevalences of B-12 deficiency in the world — estimates range from 30% to over 70% in different populations, driven largely by predominantly vegetarian diets (B-12 occurs naturally only in animal products). The consequences are serious if missed: megaloblastic anemia, peripheral neuropathy (tingling and numbness in hands and feet), balance and gait problems, cognitive impairment, infertility, and adverse pregnancy outcomes.
Unlike many deficiencies, B-12 deficiency can be silent — bloodwork may look normal early on, with only neurological symptoms (some of which become permanent if treatment is delayed). Testing is recommended for all vegetarians and vegans, anyone over 50, people with autoimmune disease (pernicious anemia), gastrointestinal surgery / bariatric surgery, chronic acid-suppressant use (PPIs, H2 blockers), or unexplained fatigue / neuropathy / cognitive change.
How to prepare
No fasting required. Continue your usual diet. If you take B-12 injections or high-dose oral B-12 supplements, the test result will be high — this does not necessarily mean you have enough at the tissue level. Tell your doctor about all supplements. If checking for deficiency, ideally test before starting any B-12 supplement or at least 4 weeks after stopping (note: stopping should only be done with your doctor's guidance).
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Vitamin B-12 (Total) (pg/mL)[1][2][3] | 200 – 900 (typical lab range; Indian guideline favours > 300 for clinical sufficiency) | < 200 pg/mL — deficient. Common in vegetarians, older adults, people on PPIs or metformin long-term, anyone with malabsorption (coeliac, IBD, Crohn's, post-gastric-bypass). 200–300 pg/mL is a "grey zone" — many guidelines treat this as functionally deficient if symptoms (neuropathy, fatigue, megaloblastic anemia) are present. Confirmation with MMA / homocysteine helps in unclear cases. | > 900 pg/mL — usually reflects recent supplementation or injection and is rarely concerning. Rarely, very high B-12 (especially without supplements) can flag liver disease (cirrhosis, hepatocellular carcinoma) or myeloproliferative disease — discuss with your doctor if persistently high without any source. |
How to read your Vitamin B-12 result
| B-12 (pg/mL) | Status | What it means | Action |
|---|---|---|---|
| < 150 | Severe deficiency | High risk of megaloblastic anemia and neurological symptoms | Likely B-12 injections (1000 mcg IM weekly × 4–6 weeks, then monthly) + dietary review |
| 150 – 199 | Deficiency | Treatment recommended | High-dose oral (1000–2000 mcg/day) or IM injections; re-test in 3 months |
| 200 – 299 | Borderline / low-normal | Often functionally deficient if symptomatic — vegetarians frequently sit here | Check MMA / homocysteine if symptoms; supplement 500–1000 mcg/day; re-test in 3 months |
| 300 – 900 | Sufficient | Healthy B-12 status | Continue dietary intake; vegetarians may still need ongoing supplementation |
| > 900 | High (usually supplementation) | Often expected after recent injection or high-dose oral B-12 | Confirm supplement source; investigate further only if unexpectedly high without supplementation |
Frequently asked questions
Why are vegetarians more likely to be B-12 deficient?
B-12 occurs naturally almost exclusively in animal products — meat, fish, eggs, dairy. Plant foods contain virtually no usable B-12. Indian vegetarians who do eat dairy get some, but often not enough; pure vegans need supplementation to avoid deficiency.
Do I need to fast for a B-12 test?
No. A B-12 test does not require fasting and can be done at any time. Continue your usual diet.
My B-12 is 250 — am I deficient?
A value of 200–300 pg/mL is a "grey zone" — labs call it normal but many clinicians treat it as functionally deficient, especially if you have symptoms like tingling, numbness, fatigue, or memory issues. If symptomatic, methylmalonic acid (MMA) or active B-12 (holotranscobalamin) testing can confirm. Many doctors will simply start a supplement and re-check in 3 months.
Can I correct B-12 deficiency with diet alone?
If the deficiency is mild and your diet allows it, increasing animal-source foods (eggs, dairy, fish, meat) helps over months. For moderate-to-severe deficiency, established neurological symptoms, or pernicious anemia (loss of intrinsic factor), supplements or injections are needed — diet alone is too slow.
Oral B-12 or B-12 injections — which is better?
For most causes of deficiency, high-dose oral B-12 (1000–2000 mcg/day) is as effective as injections, more convenient, and cheaper. Injections are preferred for severe deficiency with neurological symptoms (faster correction), pernicious anemia, malabsorption, or when adherence is a problem. Your doctor will pick based on cause and severity.
Can metformin cause B-12 deficiency?
Yes. Long-term metformin (used for diabetes) reduces B-12 absorption in about 30% of users. Anyone on metformin for over a year should have a B-12 check, especially if they also have neuropathy symptoms (which can mimic diabetic neuropathy).
How long does it take for symptoms to improve after treatment?
Blood counts and fatigue usually improve in 4–8 weeks. Neurological symptoms (tingling, numbness, gait) can take 3–6 months to improve and may not fully reverse if deficiency was prolonged — early treatment matters.
How often should I get a B-12 test if I am vegetarian?
Once at baseline, then every 1–2 years if you are not on regular supplementation. If you are on supplementation, periodic monitoring depends on your doctor — usually annual is sufficient once levels are stable.
Related Vitamins / Nutrition tests
Tests commonly ordered alongside VITAMIN B-12, or that help interpret an unexpected result.
Sources & references
- British Society for Haematology — B12 & Folate Guidelines · accessed 2026-05-29T00:00:00.000Z
- NIH Office of Dietary Supplements — Vitamin B12 · accessed 2026-05-29T00:00:00.000Z
- NIH MedlinePlus — Vitamin B12 Test · accessed 2026-05-29T00:00:00.000Z
- ICMR — Recommended Dietary Allowances for Indians 2020 · accessed 2026-05-29T00:00:00.000Z
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