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What’s The Difference Between Total B12 and Active B12?

Vitamin B12 plays an important role in the body and if you are feeling tired or weak it could be a sign you are deficient.

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There are two types of vitamin B12 in the body, these are active B12 and inactive B12, both make up Total B12. The simple difference between the two forms is that active B12 is the form used by the body.

In this blog article we explain the difference between active and total B12 and why you should check your active B12 levels.  We also outline the main symptoms of vitamin B12 deficiency.

What Is Total B12?

Total B12 is a measure of both active and inactive forms of the vitamin B12. 

Vitamin B12 is bound to two proteins, one is haptocorrin the other is transcobalamin. When vitamin B12 is bound to haptocorrin it is not taken up by cells for the body to use and is therefore an inactive form of B12 stored by the body. 

What Is Active B12?

Active B12 is when B12 binds to transcobalamin protein (known as Holotranscobalamin or HoloCT) and is made available to cells for use in the body, hence being called active B12. 

It’s the levels of active B12 you really need to be concerned with if you are worried about thyroid issues, fatigue or any other symptoms associated with a vitamin B12 deficiency.

The Problem With Testing Total B12 Levels

The most widely used B12 test on the NHS is one that checks total levels of B12, including the inactive form of it.

This means that your B12 levels might show as normal following one of these blood tests, but  in reality you could have low levels of active B12 - the version the body can actually use.

Active B12 typically makes up 10% - 30% of all the B12 in the body, so someone sitting in the “normal,” range with the widely used serum tests might actually be B12 deficient.

In other words, this sort of testing could fail to diagnose a vitamin B12 deficiency accurately.

Why Test Your B12 Levels?

The two main reasons to check your Vitamin B12 levels are:

  1. You’re concerned about a thyroid disorder
  2. You are experiencing unexplained fatigue

However, while many people are familiar with B12 testing, many aren’t familiar with or are not aware of active B12 testing and how it provides are more accurate picture of B12 within the body.

What Are The Symptoms Of Vitamin B12 Deficiency?

An active B12 test will help identify if your levels are below the normal range. Some of the symptoms of vitamin B12 deficiency include:

  1. Fatigue
  2. Anaemia
  3. Neurological features
  4. Sore tongue
  5. Bone marrow suppression
  6. Cardiomyopathy

Foods Rich In Vitamin B12

Vitamin B12 is not produced by the body so it has to be gained from your diet. Foods that are rich in vitamin B12 include:

  • Salmon
  • Trout
  • Chicken
  • Beef
  • Liver
  • Clams
  • Cheese
  • Milk
  • Yogurt
  • Eggs

Read more about good sources of B12.

Want To Find Out Your Active B12 Level?

Active B12 tests are not commonly available through the NHS, but you can gain insight into your active B12 levels quickly and easily with our home finger-prick test kit.

Simply collect a small sample of blood at home and post it direct to our UK accredited lab for analysis.  Your results will be available within 24-48 hrs on your own online personal health dashboard.  Any results outside of the normal range will be reviewed by one of our GPs who will offer advice on how to improve your levels.

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Vitamin B12 Test

If you’re feeling tired and weak a vitamin B12 test might explain why. Low levels cause fatigue, and a home B12 test will give you a quick and accurate measurement.
Vitamin B12 Test
1 Biomarkers Included
Home test to identify low and deficient levels of vitamin B12.


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