Vitamin B12 (Active) Blood Test, from our experts to you.
Dr Sam Rodgers MBBS, MRCGP

Chief Medical Officer meet our doctors

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What is vitamin B12
and what does it do?

Vitamin B12 (cobalamin) is an essential water-soluble vitamin, found mostly in animal products, such as meat, fish, milk, and eggs. It’s used to make new cells and DNA (the genetic material in all your cells), and to keep your nerves and red blood cells healthy. 

We get vitamin B12 from our diet. So, if you don't eat enough vitamin B12-rich foods, you have a higher risk of a deficiency. You can also get a deficiency if your body is unable to absorb vitamin B12 properly, due to conditions such as coeliac disease or pernicious anaemia. 

What can I learn
from an active b12 test?

Our active B12 test can tell you if you have a low level of vitamin B12 and whether you’re at risk of vitamin B12 deficiency anaemia, which affects the transport of oxygen around your body. 

Because around 70% of the vitamin B12 in your body is inactive, our test only measures your active vitamin B12 level, as this is thought to be the best early indicator of a deficiency. 

What are the symptoms of
a vitamin B12 deficiency?

A vitamin B12 deficiency can cause a wide range of symptoms including extreme tiredness, a lack of energy, muscle weakness, pins and needles, and poor memory.

These symptoms usually develop gradually but can worsen if the condition goes untreated. It’s important that B12 deficiency anaemia is diagnosed and treated early, as other conditions and potential complications can develop alongside it over time.

Low vitamin B12 levels can be detected with a blood test, and in most cases, a deficiency can be easily reversed.

What's Included?

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Vitamin B12 - active Vitamin B12 is important for production of red blood cells which carry oxygen around the body. B12 is also involved in metabolism and the nervous system and prolonged lack of vitamin B12 may cause nerve damage. Although Vitamin B12 is almost entirely found in animal-based foods, many vegetarian and vegan products, especially plant milks are now fortified with Vitamin B12.

How to prepare
for your test?

Special Instructions

Prepare for your Vitamin B12 (Active) Blood Test by following these instructions. Do not take biotin supplements for two days before this test, discuss this with your doctor if it is prescribed. Do not take vitamin B12 for two weeks prior to this test. If your B12 is prescribed ask your doctor whether to stop.

Frequently asked questions

What causes vitamin B12 deficiency?

The most common cause of vitamin B12 deficiency in the UK is pernicious anaemia, an autoimmune condition that prevents your body from absorbing vitamin B12 from food.

A deficiency can also be caused by a lack of vitamin B12 in your diet. Although this is increasingly uncommon, people who eat a diet low in dairy and animal products, such as those who eat a plant-based diet or have allergies, are at higher risk.

Other risk factors include taking certain medications such as metformin and omeprazole, having a gut autoimmune disease like Crohn's or coeliac disease, and being over 60.

How much vitamin B12 do I need?

The recommended daily amount of vitamin B12 varies depending on your age. The table below gives the daily average vitamin B12 amount recommended at each life stage.

AgeRecommended amount (mcg)
1 year0.5
2-3 years 0.5
4-6 years0.8
7-10 years1.0
11-14 years1.2
15-18 years1.5
19+ years1.5

How can I improve my vitamin B12 level?

In some cases, making changes to your diet can improve your vitamin B12 level. Foods that are rich in vitamin B12 include meat, fish, eggs, and dairy products.

However, there are plant-based sources like yeast extract (such as Marmite) and fortified breakfast cereals. Find out more about plant-based diets and nutrition.

You may need to take a supplement to improve your level, and you should follow your GP’s advice carefully regarding treatments.

How can I check my vitamin B12 level at home?

You can use our finger-prick B12 home test kit to check your level. This includes a full lab analysis of your blood sample and expert medical advice on any next steps. You can view your results and doctor’s comments on your MyMedichecks dashboard.

What’s the difference between active vitamin B12 and total vitamin B12?


Measuring your total vitamin B12 might seem like the best way to check for a deficiency. However, only around 30% of the vitamin B12 in your body is available to use (known as active vitamin B12), while the rest is stored in an inactive form.

This means a normal total vitamin B12 result (including both active and inactive forms) could be misleading and may hide a deficiency. At Medichecks, we only measure your active vitamin B12 level to give you the most accurate result. Find out more about the difference between active and total vitamin B12.


What is pernicious anaemia?


Pernicious anaemia is an autoimmune disease that affects your body’s ability to absorb vitamin B12, causing vitamin B12 deficiency anaemia. Symptoms include feeling tired all the time, breathlessness, and mouth ulcers.

You’re more at risk of pernicious anaemia if you have a family history of the disease or another autoimmune condition, such as type 1 diabetes or a thyroid condition. If you’re concerned about pernicious anaemia, you can take a Pernicious Anaemia Blood Test.