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Laboratory values: How do you recognise a vitamin B12 deficiency in the blood?

Vitamin B12 deficiency occurs relatively frequently and is considered a problem worldwide. Women and the over 65 age group in particular are often deficient. It is assumed that 10-30% of the older population group has a B12 deficiency. Vitamin B12 is the only water-soluble vitamin that is stored in the liver. As we only need very small amounts of this vitamin every day, the stores last for around 2-5 years. An inadequate vitamin B12 supply is therefore not immediately noticeable in a blood test. To determine a B12 deficiency in the blood count, other laboratory values must therefore be considered than the vitamin B12 serum level.

Table of contents
  • What is vitamin B12?
  • What is the role of vitamin B12 in the body
  • Who is affected by a vitamin B12 deficiency?
  • Risk factors for a vitamin B12 deficiency
  • Vitamin B12 blood test: What should I look out for
  • Vitamin B12 laboratory values: How a deficiency shows up

What is vitamin B12?

Various forms of cobalamin are summarised under the term vitamin B12. The forms active in the body are methylcobalamin and adenosylcobalamin. Cobalamin is the chemical name for B12, as all compounds active as B12 contain a cobalt atom. Other forms are often found in food supplements.

You can read more about the different forms of B12 in the article Vitamin B12 supplementation: cyanocobalamin vs. methylcobalamin.

What functions does vitamin B12 have in the body?

Vitamin B12 is often referred to as the "nerve protection vitamin" as it plays an important role in the nervous system. The vitamin is involved in the regeneration and new formation of nerve fibre sheaths. A typical sign of a vitamin B12 deficiency can therefore be tingling or numbness in the hands and feet. However, vitamin B12 is not only important for strong nerves, but also for haematopoiesis and cell division. Listlessness, anaemia, exhaustion or an increased susceptibility to infections can therefore also indicate an inadequate supply.

Who is affected by a vitamin B12 deficiency?

Vitamin B12 is produced exclusively by microorganisms. However, it also finds its way into animal foods via the enrichment of animal feed. People who follow a plant-based diet - i.e. vegan or vegetarian - must take B12 via vegan food supplements (such as our vitamin B12 lozenges or our B12 drops).

As the absorption of B12 decreases with increasing age, people aged 65 and over also belong to the risk group. People who frequently have stomach problems in particular should have their vitamin B12 blood levels checked regularly. In order to absorb vitamin B12, we need intrinsic factor, a glycoprotein that is formed in the gastric mucosa. In the case of chronic inflammatory stomach diseases, a deficiency can therefore occur despite sufficient vitamin B12 intake, as the vitamin B12 supplied cannot be absorbed. In higher doses, B12 can also be absorbed via passive diffusion through the oral mucosa. B12 supplements in the form of lozenges or drops are therefore very popular as they can improve absorption.

Nutri-Plus vitamin B12 lozenges and drops

Our delicious B12 lozenges (sucked or chewed) provide the body with an optimal supply of vitamin B12. You can also find nutri+ B12 drops in the shop, which contain the two active B12 forms methylcobalamin and adenosylcobalamin. These do not need to be metabolised in the body first and have a high bioavailability.

Risk factors for a vitamin B12 deficiency

  • Vegan/vegetarian diet
  • Age group 65 years and older
  • Pregnant women
  • Kidney and liver diseases
  • Autoimmune diseases or HIV infection
  • Gastrointestinal diseases (e.g. gastritis, Crohn's disease, ulcerative colitis)
  • Taking certain medications (e.g. acid blockers, ACE inhibitors, statins, metformin)

Vitamin B12 blood test: What do I need to look out for?

As the level of cobalamin in the blood can be kept relatively constant due to the stores in the liver, the total vitamin B12 value in the serum or plasma does not provide a meaningful reflection of the B12 supply. Only when the stores in the liver are exhausted does a deficiency become apparent. A better biomarker is holo-transcobalamin (holo-TC). Holo-TC is also known as active B12. After being absorbed from the intestine, vitamin B12 is transferred to the transport protein transcobalamin II, among others, which circulates as holo-TC in the blood until it is absorbed by the cells. A low holo-TC in the blood is therefore the first indication that the stores are already depleted and the supply is insufficient.

Functional parameters: MMA and homocysteine

To be on the safe side, the value of methylmalonic acid (MMA) and/or homocysteine in the blood can also be determined. Methyl- and adenosylcobalamin are cofactors in various metabolic reactions. If there is an intracellular deficiency, these reactions cannot take place or can only take place inadequately. The initial substrates - in this case methylmalonic acid and homocysteine - accumulate in the blood and can thus indirectly indicate a B12 deficiency. MMA and homocysteine are therefore called functional parameters. To rule out a deficiency with certainty, the holo-TC value and one of these functional biomarkers should be determined. However, it should be noted that homocysteine is not a specific B12 marker, but can also indicate a folic acid or B6 deficiency.

B12 blood values: regular check

By determining the holo-TC and MMA/homocysteine levels, a deficiency can be detected even if there are no clinical symptoms (e.g. anaemia or nerve damage). High-risk groups should therefore have their vitamin B12 blood levels (holo-TC and MMA) analysed every two years or so.

Vitamin B12 laboratory values: how a deficiency shows up

The following laboratory values are often considered when diagnosing a B12 deficiency. Although the total B12 value is not conclusive, it is still frequently carried out as it is particularly cost-effective. Before the examination, it should therefore be discussed with the doctor which B12 supply parameters will be determined and what additional costs will be incurred if the functional parameters are determined.

Vitamin B12 serum level

Standard value: 200 to 1000 ng/l A definite B12 deficiency is said to be present from values < 200 ng/l (< 150 pmol/l), but a functional B12 deficiency can also be present before this.

Holotranscobalamin blood value (Holo-TC)

Standard value: > 50 pmol/l
Below a value of 35 pmol/l there is a definite deficiency.

Methylmalonic acid (MMA) blood value

Standard value: 50 to 300 nmol/l
Homocysteine blood value
Standard value: < 10 µmol/l

Conclusion: B12 blood values - how do I recognise a deficiency? To assess the supply, the status parameters total vitamin B12 and holo-TC as well as functional parameters MMA and homocysteine can be determined in a B12 blood test. Note: The vitamin B12 serum level alone is not meaningful.

Sources: Causes and early diagnosis of vitamin B12 deficiency. Dtsch Arztebl 2008; 105(40): 680-5 Vitamin B12 for the brain. The consequences of vitamin B12 deficiency are underestimated. DAZ 2012; 8:70