What is a vitamin B12 blood test?

The vitamin B12 blood test measures the amount of vitamin B12 in your blood. Your folate level is usually tested at the same time.

Vitamin B12 is one of the B group of vitamins. It is also known as cobalamin.

Vitamin B12 is vital for:

• making new blood cells
• cell and tissue repair
• nerve health
• generation of new DNA

Vitamin B12 and folate work together to help with cell functioning.

Your body cannot make vitamin B12 by itself and needs to get vitamin B12 in through your diet. Most vitamin B12 in your diet comes from animal products, such as:

• meat
• poultry
• seafood
• milk
• cheese
• eggs

If you do not consume enough vitamin B12, your doctor might recommend supplements.

When is a vitamin B12 blood test used?

Your doctor may refer you for a vitamin B12 blood test if you:

• have anaemia (lack of red blood cells) or an abnormal blood test
• have symptoms that suggest a low level of vitamin B12 (dizziness, weakness, tiredness or neuropathy)
• have a medical condition that affects your ability to absorb vitamin B12 from your gut
• follow a vegan or vegetarian diet
• experience changes to your mental health
• are pregnant or breastfeeding

Low levels of vitamin B12 can cause a type of anaemia called macrocytic anaemia. This is when your red blood cells don't grow normally. It can lead to neuropathy, a type of nerve damage that makes your hands and feet tingle or feel numb.

You may develop vitamin B12 deficiency if you have a condition called pernicious anaemia. This is when your immune system destroys the molecules that your body produces to absorb vitamin B12.

If you are pregnant or breastfeeding, you may need extra folate and B vitamins to help with the growth and development of your baby.

Where can I get a vitamin B12 blood test?

You usually need to go to a pathology collection centre to get a vitamin B12 blood test. Your doctor will recommend one near you. You will need a referral from your doctor for this blood test.

Sometimes, your doctor will collect blood for testing in their clinic. Blood tests are also routinely done in hospitals.

How do I prepare for a vitamin B12 blood test?

What you need to do before your test will depend on the blood test you're having.

You may need to fast (avoid eating) for 6 to 8 hours before your blood test, to prevent food or drink from affecting your result. In this case, you can usually continue to drink water.

Most people have the test in the morning, so it doesn't interfere with their meals.

If you take vitamin B12 supplements, do not take them before the test.

If you are having other blood tests done at the same time, you may need to prepare. Check with your doctor or the pathology collection centre if there is anything you need to do before your blood test.

What happens during a vitamin B12 blood test?

A health professional will take a sample of blood from a vein in your arm. The blood will then be sent to a laboratory for testing.

What do my vitamin B12 blood test results mean?

A low vitamin B12 blood test result means that your body lacks this vitamin.

Low levels could also be a sign of folate deficiency. B12 helps your body use folate to make new proteins and healthy red blood cells. If your B12 level is low, it might also mean your folate is low. Your doctor may recommend additional tests to check.

Your doctor may also refer you for further tests to understand why your vitamin B12 levels are low.

Alone, the results do not provide information about:

• what is causing your B12 or folate deficiency
• how severe it is
• your stored levels of B12 compared to your available levels

Discuss your blood test results with your doctor to understand what they mean for you.

Resources and support

About vitamin B12 testing

See Pathology Tests Explained for more information on vitamin B12 testing.

About blood testing

Visit healthdirect's 'Guide to blood testing' to learn more about blood tests in general, including information about:

• what to consider before having the test
• what happens during a blood test
• the accuracy of your results
• the costs of your blood tests

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available 24 hours a day, 7 days a week.'