What is vitamin B12?
Vitamin B12, cobalamin, does two things you cannot do without. It is needed to make DNA, and so for every cell that divides, with the making of red blood cells as the place where that shows first. And it is needed for the insulating layer around your nerves, which is why a deficiency starts with tingling and numbness in feet and hands. B12 works together with folate in this, and the two clear homocysteine together. B12 comes almost only from animal food: meat, fish, eggs and dairy. Plants do not make it. Its uptake is a relay, too. Stomach acid frees B12 from food, the stomach lining makes a protein, intrinsic factor, that binds to B12, and that package is only absorbed in the last stretch of the small intestine. If one of those steps falters, uptake drops, even with a plate full of meat. What you do absorb, your liver keeps for years, and that is why a deficiency develops slowly and stays unnoticed for a long time. Your report shows vitamin B12 in pmol/L. Normal is about 175 to 569 pmol/L where the labs overlap, with a lower limit that differs per lab. The number measures the total B12 in your blood, and that does not always say whether your cells have enough; methylmalonic acid and homocysteine fill that gap.
Why is vitamin B12 relevant?
A B12 deficiency is one of the most missed deficiencies, because it comes so slowly. Your liver holds a store of years, so anyone who switches to plant-based eating or starts antacids notices nothing for a long time. Then the symptoms come: tiredness that does not pass, tingling and numbness in feet and hands, an unsteady feeling when walking, forgetfulness, low mood, a sore tongue. The anaemia in the textbooks often comes only later, or not at all. And the part you least want to miss, the nerve damage, can become permanent if the deficiency lasts long enough. That is the reason to know your B12 before there are symptoms, if you belong to one of the groups in which uptake falters. Those groups are clear. Anyone who eats vegetarian or vegan takes in too little and needs a supplement, full stop. Anyone on antacids no longer frees B12 from food. Anyone on metformin absorbs less in the gut. Anyone getting older makes less stomach acid and less intrinsic factor. Anyone using nitrous oxide puts the B12 that is there out of action, and with regular use that gives nerve damage within months at a normal store. And in pernicious anaemia the production of intrinsic factor is lost to an autoimmune reaction; no food helps then. The good part is that a deficiency is very reversible, and cheap. A high-dose tablet works in almost everyone, even with poor uptake, because a small share always gets in without intrinsic factor; injections exist for anyone in whom that fails. The earlier you start, the more of the nerve symptoms reverse.
Vitamin B12 reference ranges
What counts beside the number:
- How you eat, and whether you use antacids or metformin, because that is where it usually starts
- Symptoms such as tingling, numbness, tiredness or forgetfulness, which weigh more than the number
- Methylmalonic acid and homocysteine, which show whether your cells are running short
- Folate, which works in the same step and gives the same blood picture
- Your blood count, because a deficiency makes the red cells larger
- Whether you have already started topping up, because then the total B12 says nothing more
The band above is where the labs overlap, and for B12 it is mainly the lower limit that differs per lab. The grey zone, roughly between the lower limit and 250 pmol/L, is the zone where the total B12 says little and methylmalonic acid and homocysteine make the difference. The values are the same for men and women and fall slowly with age, because uptake declines. Once you top up, the total B12 can no longer be read as a measure of the deficiency.
What Dutch labs actually use
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, per lab
| Laboratory | 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/LDecision limit |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Vitamin B12 high or low: what it means
A low B12 means the supply falls short or the uptake falters. In order of how often it occurs: plant-based eating, antacids, getting older, metformin, and then heavy drinking, stomach surgery or gut disease, pernicious anaemia and nitrous oxide. A value below the lower limit with symptoms is a reason to top up; a value below the lower limit without symptoms is a reason to look at where it comes from and to adjust your diet or add a supplement. In between lies the grey zone, roughly between the lower limit and 250 pmol/L. The total B12 in your blood says little there, because part of that B12 is bound to a protein that does not hand it over to your cells. Methylmalonic acid and homocysteine show whether your cells are running short: methylmalonic acid rises only with a B12 deficiency, homocysteine also with a folate or B6 deficiency. A normal B12 with symptoms and a high methylmalonic acid is a deficiency; a low B12 with a normal methylmalonic acid and no symptoms usually is not. A high B12 is almost always a supplement or an injection and no cause for concern; what you have too much of, you pass in the urine. Without a supplement a high B12 is rare and a look at the liver belongs with it. Take note: once you have started topping up, the total B12 shoots up while the cells are not yet refilled. The number then says nothing more about the deficiency; methylmalonic acid and the symptoms do. What you do about it: if you eat plant-based, take a supplement and treat it as a fixed habit. If you take antacids or metformin, or are over sixty, have B12 measured now and then. Leave nitrous oxide alone. Read B12 beside folate, methylmalonic acid, homocysteine and your blood count, because a deficiency makes the red cells larger, and compare over time at the same lab.
What lowers it
You take in too little, or the relay of the uptake falters somewhere.
| Cause | How often |
|---|---|
| Plant-based dietPlants make no B12; anyone eating vegetarian or vegan needs a supplement, and the store in the liver hides the deficiency for years | Often |
| AntacidsWithout stomach acid B12 is not freed from food; with long-term use the value slowly falls | Often |
| Older ageWith the years the stomach lining makes less acid and less intrinsic factor, the protein that helps B12 into the gut | Often |
| MetforminReduces the uptake of B12 in the gut; with long-term use an occasional check is sensible | Often |
| Heavy drinkingDamages the stomach lining and goes together with a less varied diet | Sometimes |
| Stomach surgery or gut diseaseAfter a gastric bypass or with disease of the last stretch of small intestine, as in Crohn's, uptake is lost; a supplement or injection is then a fixed habit | Sometimes |
| Pernicious anaemiaAn autoimmune reaction against the stomach lining that removes intrinsic factor; no food helps then, injections or a high dose do | Sometimes |
| Nitrous oxidePuts the B12 that is there out of action; with regular use that gives nerve damage within months, sometimes at a normal value | Sometimes |
What raises it
Almost always what you take yourself or were injected with; rarely the liver.
| Cause | How often |
|---|---|
| Supplements or injectionsThe total B12 shoots up as soon as you top up, even while the cells are not yet refilled; what you have too much of, you pass in the urine | Often |
| Liver diseaseA damaged liver releases its store of B12 into the blood; a high B12 without a supplement is a reason to look at the liver | Rare |
How does a vitamin B12 blood test work?
- Referral
- Not needed. You can have vitamin B12 measured yourself, and it is one of the most useful values for anyone eating plant-based or using antacids.
- Fasting
- Not needed; the total B12 barely moves with a meal. Do have blood drawn before you start topping up, because afterwards the number says nothing more about the deficiency.
- The draw
- One tube of blood from a vein in your arm. Folate, methylmalonic acid and a blood count come from the same draw.
- The result
- A single number in pmol/L. Below your lab's lower limit is low, above about 250 the store is fine, and in between lies the grey zone where methylmalonic acid settles it.
- Repeating
- While topping up not the B12 itself, but the symptoms and where needed methylmalonic acid after three months. Anyone eating plant-based or using antacids or metformin measures every few years.
- Which test
- Vitamin B12 is in the Iron & fatigue test (€99) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is vitamin B12?
The vitamin you need to make DNA, and so red blood cells, and for the insulating layer around your nerves. It comes almost only from animal food: meat, fish, eggs and dairy. Uptake is a relay of stomach acid, a protein from the stomach lining and the last stretch of small intestine, and if one of those steps falters a deficiency develops even with a plate full of meat. Your liver keeps a store of years.
What is a normal vitamin B12 level?
About 175 to 569 pmol/L where the labs overlap, with a lower limit that differs per lab. Above about 250 pmol/L your store is fine. Between your lab's lower limit and that 250 lies a grey zone in which the number says little, and there methylmalonic acid and your symptoms decide.
What does a low vitamin B12 mean?
That the supply falls short or the uptake falters: plant-based eating, antacids, getting older and metformin are the most common reasons, then heavy drinking, stomach surgery, pernicious anaemia and nitrous oxide. With symptoms such as tingling, tiredness or forgetfulness topping up is called for, and the sooner the better, because nerve damage can become permanent. Without symptoms it is a reason to look at your diet and your medicines and to have methylmalonic acid measured alongside.
What is the grey zone for B12?
The zone between your lab's lower limit and about 250 pmol/L. The total B12 in your blood is partly bound to a protein that does not hand it over to your cells, so a number in that zone can be either a deficiency or a perfectly good store. Methylmalonic acid makes the difference: it rises only when the cells have too little B12. High methylmalonic acid with symptoms is a deficiency, normal methylmalonic acid without symptoms usually is not.
Is a high vitamin B12 harmful?
No. A high value is almost always a supplement or an injection, and what you have too much of, you pass in the urine. The number is misleading then, though: the total B12 shoots up as soon as you top up, while the cells need months to recover. Look at the symptoms and at methylmalonic acid then, not at the B12. A high B12 without a supplement is rare and belongs together with a look at the liver.
Why do my symptoms not match my B12 level?
Because the total B12 does not measure what your cells can use. A normal number with tingling, tiredness or forgetfulness can still be a deficiency, especially in the grey zone and in anyone using nitrous oxide, and then methylmalonic acid shows it. The other way round, a low value without symptoms and with a normal methylmalonic acid is usually not a deficiency. The symptoms and methylmalonic acid therefore weigh more than the number alone.
Can I keep my vitamin B12 up myself?
Yes. If you eat meat, fish, eggs and dairy, it comes by itself. If you eat plant-based, a supplement is a fixed habit, because plants make no B12. If you take antacids or metformin, or are over sixty, have B12 measured every few years. With a deficiency a high-dose tablet works in almost everyone, even with poor uptake; injections exist for anyone in whom that fails. And leave nitrous oxide alone.
Do I need to fast for a vitamin B12 test?
No, the total B12 barely moves with a meal. What does count: have blood drawn before you start topping up, because afterwards the number says nothing more about the deficiency. Folate, methylmalonic acid and a blood count come from the same draw.
Which tests include vitamin B12?
Vitamin B12 is in the Iron & fatigue test (€99, also as an add-on for €15), in the True vitamin B12 test (€119, also as an add-on for €69), in the comprehensive test (€229) and in .
Related biomarkers
Read on
Sources
- 1.Unilabs, test catalogue (Dutch): vitamin B12. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): vitamin B12. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): vitamin B12. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): vitamin B12. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
Read about our scientific approachShare