What is vitamin B12 deficiency?
Vitamin B12 is needed in two places at once. Fast-dividing cells, such as the precursors of red blood cells, need it to make DNA; without enough B12 the cells become too large and too scarce. And the nerves need it for their insulating layer; there a deficiency gives tingling, numbness and unsteady walking. Those two tracks do not run in step, so the complaint side can run months ahead of the blood count. B12 is only in animal products, and to absorb it the gut needs a protein from the stomach. That is why the most common causes are a stomach that no longer makes that protein, through an autoimmune inflammation or simply through getting older, years of acid suppressants or metformin, a stomach operation or bowel disease, and plant-based eating without fortified products or a supplement. Nitrous oxide makes the B12 you already have inactive in one go. Measuring is harder here than it seems. The liver keeps a store that lasts for years, and total B12 in your blood does not always say how much of it the cells can really use. That is why there is a grey zone in which the number alone does not answer the question, and methylmalonic acid (MMA) decides: it accumulates as soon as cells genuinely run short of B12.
Which blood values show vitamin B12 deficiency?
Every value below has its own page with the reference ranges of four Dutch labs.
| Value | What it shows | Points here when |
|---|---|---|
| Vitamin B12defining | The store gauge in your blood. With a grey zone in which the result alone does not say enough. | low |
| MMA | Accumulates as soon as cells genuinely run short of B12. The decider in the grey zone. | high |
| MCV | The average cell size. In this deficiency red blood cells come out larger. | high |
| RDW | Rises when old and new cells mix, also in a combined deficiency with iron. | high |
| Hemoglobin | Falls late. The nerve complaints can be there before the Hb moves. | low |
What are the symptoms of vitamin B12 deficiency?
These complaints are described for vitamin B12 deficiency in guidelines and research. None of them is exclusive to it: the same complaints fit many other explanations, and an abnormal value can exist without any of them.
A slightly lowered B12 often goes without complaints, and complaints can exist at a value that looks normal. Precisely that poor correlation is why the grey zone is worked out with methylmalonic acid instead of guessed away.
- Tingling or numbness in hands or feetin the guideline
Nerve complaints are why a B12 deficiency is taken seriously; always discuss them with your GP.
- Unsteady or wobbly walkingin the guideline
- Burning or painful tonguein the guideline
- Tirednessin the guideline
How tired you are says little about how low your B12 is: complaint and measured value track each other remarkably poorly here.
Also described at iron deficiency, anaemia, underactive thyroid, low testosterone.
- Forgetfulness or slower thinkingin research
Also described at iron deficiency, underactive thyroid, low testosterone.
- Low mood or irritabilityin research
Also described at underactive thyroid, low testosterone.
- Looking palein the guideline
Belongs to the stage where the deficiency leads to anaemia; that page explains this complaint.
A complaint points in more than one direction, and a measurement explains no complaint: blood testing shows where your values stand, the reading and the diagnosis belong with your GP. The complaint list follows the Dutch GP guideline on anaemia (NHG).
What causes vitamin B12 deficiency?
Absorption
By far the most common route: the stomach or bowel no longer gets B12 in.
- Pernicious anaemia, in which the immune system disables the uptake factor
- Long-term use of acid-suppressing medication or metformin
- After stomach or bowel surgery
- Declining stomach function at older age
Intake
B12 comes almost exclusively from animal products.
- Vegan or largely plant-based eating without a supplement
Consumption and other
Rarer, but sometimes surprisingly fast.
- Nitrous oxide use, which disables the B12 you already have
- Pregnancy and breastfeeding, in which demand rises
What is vitamin B12 deficiency confused with?
Each with the one value that tells the two apart.
Folate deficiency
Gives the same blood picture with large red blood cells. That is why folate and B12 are measured together; the nerve complaints belong to B12 alone.
Distinguishing value: Folate
Anaemia
A B12 deficiency is one of the routes into anaemia, but the nerve complaints can run ahead of the blood count. A normal Hb does not rule this deficiency out.
Distinguishing value: Hemoglobin
Iron deficiency
Both bring tiredness and paleness, but MCV points opposite ways: small in iron, large in B12. In a combined deficiency MCV can look normal and RDW gives the mix away.
Distinguishing value: MCV
What you do about vitamin B12 deficiency
Replenish along the route that fits the cause. If you eat plant-based, fortified products or a supplement are the only source, and a daily tablet of a few micrograms up to a weekly high dose keeps the store up; anyone who eats meat, fish, eggs and dairy naturally takes in enough. If absorption is the problem, through a stomach that no longer makes the absorption protein, acid suppressants, metformin or a stomach operation, a high dose of tablets still works in most people, because a small part is absorbed without that protein; injections are the way with nerve complaints or if tablets do not take. Stop nitrous oxide, because that undoes every refill. Look at your medicines: anyone who uses acid suppressants or metformin for years should have B12 measured once a year and replenish as standard if needed. Have folate measured with it, because a deficiency of that gives the same blood count, and never replenish folate alone with a B12 deficiency, because that hides the anaemia while the nerves carry on. Measure methylmalonic acid before you start, because afterwards it falls within weeks and you no longer see where you stood, and measure again after three months: the blood count recovers in weeks, the nerve complaints in months, and what has not recovered after a year usually stays.
From which vitamin B12 does a lab call it low?
This is what the four largest Dutch labs publish themselves, side by side.
175 – 569pmol/L
Between 133 and 175 and between 569 and 675 it depends on the lab, because each sets its limits on its own method and population. Above 675 every lab calls it abnormal.
every lab calls 175 – 569 pmol/L normal. Between 133 and 175 and between 569 and 675 it depends on the lab.
Every age group per lab
| Lab | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Adults | 175–672 pmol/L |
| Star-shl2026 | All ages | 148–584 pmol/L |
| Certe2026 | Men from 18 yrs | 145–569 pmol/L |
| Women from 18 yrs | 145–569 pmol/L | |
| Clinical Diagnostics2026 | Adults | 133–675 pmol/L |
| Deficient | < 108 pmol/L |
How to get vitamin B12 deficiency measured
- Fasting
- No fasting needed. A B12 supplement taken the same day can raise the result though.
- Material
- Venous blood, drawn at one of our collection points.
- Results
- Results within 24 hours of analysis, in the app.
- Referral
- No referral from a GP required.
- Which test
- The Iron & fatigue test (€99, single test) measures the values on this page.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
From which B12 value do you speak of a deficiency?
Below 133 pmol/L it is a deficiency for everyone, and above that it differs: the lower limit runs from 133 to 175 pmol/L, so the same 150 is a deficiency on one report and normal at the other three. Between 175 and 245 is a grey zone in which the number alone does not answer the question; there methylmalonic acid decides, which rises as soon as the cells genuinely run short. Below 108 there is a deficiency in everyone.
When is methylmalonic acid (MMA) measured?
When B12 falls in the grey zone and the question stays open, and with complaints that fit a deficiency while B12 looks normal. Methylmalonic acid accumulates as soon as cells have too little B12 to convert it, and so measures the effect of the deficiency instead of the store in the blood. Measure it before you start replenishing, because afterwards it falls within weeks.
Can you have a B12 deficiency with a normal blood count?
Yes. The nerve side and the blood side do not run in step: tingling, a burning tongue or unsteady walking can come months before large red blood cells or a falling haemoglobin. Anyone who checks only the blood count misses that early stage, and precisely that stage recovers best. That is why B12 itself, with methylmalonic acid beside it, weighs more here than the blood count.
What about B12 with plant-based eating?
B12 comes almost only from animal products; anyone who eats plant-based depends on fortified products or a supplement, and that is the only way to stay ahead of a deficiency. The deficiency builds slowly because the liver has a store for years, so complaints come late. If you measure while already supplementing, you mainly see the supplement back, and that is a real answer: it shows whether your dose is enough.
Can nitrous oxide cause a B12 deficiency?
Yes, and quickly. Nitrous oxide makes the B12 you already have inactive in one go, so nerve complaints can arise within weeks, even with a store that was in order at first. The blood value can then still look normal while the body is effectively without; methylmalonic acid does show it. Regular use and tingling together are reason to stop and to measure, because nerve damage that stays does not recover.
Sources
- 1.NHG-Standaard Anemie. 2024. richtlijnen.nhg.org
- 2.Unilabs test directory, vitamin B12. 2026. bepalingenklapper.nl
- 3.Star-shl test directory, vitamin B12. 2026. star-shl.nl
- 4.Certe test directory, vitamin B12. 2026. bepalingenwijzer.certe.nl
- 5.Clinical Diagnostics test guide, vitamin B12. 2026. clinicaldiagnostics.nl
This page explains what a result means. It is not a diagnosis and not treatment advice. Discuss complaints or an abnormal value with your doctor.
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