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  • Also Known As:
  • Cobalamin Test
  • Pernicious Anemia Test
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Test Quick Guide

Vitamin B12 testing measures the level of vitamin B12 in your blood. Having a vitamin B12 deficiency, or a low level of this essential vitamin, can cause a range of health issues, including anemia and nervous system problems.

Vitamin B12 levels may be low for a number of reasons, including inadequate dietary intake, the use of certain medications, advanced age, or conditions that make it harder for the body to absorb vitamin B12 from your food.

Testing for vitamin B12 requires a sample of blood. Measuring your vitamin B12 level helps your health care provider to diagnose a possible deficiency and recommend appropriate treatment, if needed.

About the Test

Purpose of the test

The purpose of vitamin B12 testing is to determine whether you have a deficiency or a lower-than-normal level of B12 in your body. Sometimes a vitamin B12 level will be tested by itself and other times it will be measured along with other tests for the purposes of diagnosing or monitoring certain health problems.

Diagnosis

Vitamin B12 testing may be ordered to determine the cause of a patient’s symptoms. It may also be ordered after an abnormal result on a different blood test to learn more about an individual’s health. Diagnostic purposes for vitamin B12 testing include:

  • Evaluating symptoms of anemia, a blood disorder marked by a loss of normal red blood cells.
  • Following up after an abnormal blood test that suggests megaloblastic anemia, a type of anemia where red blood cells are unusually large and function abnormally.
  • Determining the cause of symptoms related to the nervous system, including mental changes, weakness, loss of balance or numbness, pain, and tingling in the arms and legs.

Monitoring

Vitamin B12 testing may also be used for monitoring a patient’s health over time. Checking blood levels of vitamin B12 may be done:

  • To evaluate how well-nourished a person is, especially if they have a disease that makes it harder to absorb nutrients from food.
  • To monitor people who are being treated for a previously diagnosed vitamin B12 deficiency.

Screening

Screening is testing that is performed before there are visible symptoms of a health problem, like a vitamin B12 deficiency. At this time, there are no guidelines regarding screening of asymptomatic people for vitamin B12 deficiency.

However, doctors may choose to check vitamin B12 levels in people with certain risk factors that put them at a higher risk of a deficiency, such as the elderly or people who follow a vegan diet, which does not include any foods from animal sources.

What does the test measure?

Vitamin B12 is a nutrient that is important for many aspects of human health. Adequate levels of vitamin B12 are needed for your body to maintain a healthy nervous system, make red blood cells, and create DNA, the genetic material present in all of our cells.

Vitamin B12 occurs naturally in animal proteins, such as red meat, fish, poultry, eggs, and dairy. Other foods, like breakfast cereals, nutritional yeast, and some plant milks, may be fortified with vitamin B12. This vitamin is also available as a supplement and as a prescription medication.

In food, vitamin B12 is bound to protein. In order for your body to absorb it, the vitamin must be released from the protein. As your body digests food, enzymes in your digestive tract separate vitamin B12 from these proteins. The freed vitamin B12 then combines with a protein made by your body called intrinsic factor, which is secreted by cells in the stomach. Together, vitamin B12 and intrinsic factor are absorbed in the lower end of the small intestine.

When should I get vitamin B12 testing?

Vitamin B12 testing is usually performed when you have symptoms of a vitamin B12 deficiency, such as anemia or nervous system problems. Some people are at a greater risk of having a vitamin B12 deficiency due to their age or preexisting health conditions and may undergo regular vitamin B12 testing to check whether their B12 levels are normal.

The following information describes several circumstances in which vitamin B12 testing may be recommended by a doctor.

Anemia

Anemia is a condition in which your body does not have enough healthy red blood cells. Red blood cells carry oxygen to your body tissues. When you don’t have enough healthy, properly functioning red blood cells, you may have symptoms like:

  • Fatigue
  • Difficulty concentrating
  • Pale skin
  • Shortness of breath
  • Diarrhea
  • Nausea or vomiting
  • Loss of appetite

A vitamin B12 deficiency can lead to a type of anemia known as megaloblastic anemia. In megaloblastic anemia, the red blood cells are large, underdeveloped, and abnormally shaped. These abnormal red blood cells, called megaloblasts, do not function normally.

Megaloblasts may be detected through routine blood testing before a person develops symptoms of anemia. When this happens, follow-up testing is typically performed, including a vitamin B12 test.

Nervous system symptoms

Your health care provider may recommend a vitamin B12 test to determine if a low level of vitamin B12 is causing nervous system symptoms. These symptoms may include:

  • Neuropathy, which is a nerve problem that causes pain, numbness, tingling, and muscle problems
  • Weakness
  • Poor balance
  • Confusion
  • Changes in the way a person walks
  • Dementia, a condition that affects mental functions such as memory and language skills

Risk factors

Certain factors make an individual more likely to have a vitamin B12 deficiency. Your doctor may order vitamin B12 testing for you if you have one or more of the following risk factors:

  • Age over 75 years
  • Decreased intake of animal proteins, including vegetarian or vegan diets
  • Medication interactions with drugs that interfere with vitamin B12 absorption, including histamine blockers, proton pump inhibitors, metformin and nitrous oxide
  • Decreased nutrient absorption due to stomach or intestinal surgery, including surgery for weight loss or cancer
  • Decreased absorption due to diseases of the stomach and small intestine, such as celiac disease or Crohn’s disease
  • Pancreatic insufficiency, a condition that can affect how well enzymes are able to separate vitamin B12 from food proteins

Finding a Vitamin B12 Test

How to get tested

Vitamin B12 testing is most often performed at the doctor’s office or another medical setting like a laboratory or hospital. Vitamin B12 tests are normally prescribed by a doctor but may be available without a doctor’s orders at a walk-in lab or through an at-home test kit.

Can I take the test at home?

Several test kits are commercially available that allow you to collect a sample for vitamin B12 testing at home. Some kits test only your vitamin B12 level. Others test B12 in combination with other vitamins.

These kits may be purchased online and include the materials you need to obtain a sample of blood using a finger prick, which you return to the manufacturer for testing. Your test results are available after a few days via a secure online platform.

At-home testing is convenient and allows you to participate in your own health care. However, at-home tests cannot take the place of working with a health care provider. If you have symptoms or are worried that you may have a low level of vitamin B12, be sure to share your concerns with a doctor or nurse.

If an at-home test detects an abnormal vitamin B12 level, your doctor is likely to retest your vitamin B12 and follow up with additional testing if the second vitamin B12 test is also abnormal.

How much does the test cost?

The cost of vitamin B12 testing may vary depending upon factors such as where the test is performed and whether you have health care coverage.

Insurance will usually cover the cost of vitamin B12 testing if your health care provider orders it to diagnose or monitor a medical condition. You can check with your doctor or nurse, the lab, or your health insurance company to learn more about what, if any, testing costs you are responsible for.

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Taking a Vitamin B12 Test

Vitamin B12 testing requires a blood sample, which is usually taken from your arm in a medical office, health clinic, hospital, or lab.

Before the test

Before taking a vitamin B12 test it is important to fast for 6-8 hours, which means you must avoid eating and drinking anything other than water.

Since some medications can affect the results of the vitamin B12 test, you should ask your health care provider if you need to temporarily discontinue any of the medications you normally take.

During the test

During a vitamin B12 test, a small sample of blood is usually taken from a vein in your arm.

The health care provider drawing your blood sample may tie a band around your upper arm to make it easier to see where your veins are. Next, they will clean the area where the needle enters your skin. A needle attached to a sample tube will be inserted into your vein, and a small quantity of blood will be drawn into the tube. You may feel a slight sting when the needle enters your skin.

The process of taking a blood sample usually takes less than a minute.

After the test

You may be asked to apply gentle pressure to the site where the blood was removed with a piece of cotton, gauze, or bandage. Next, a bandage is applied to the site where blood was extracted.

Providing a blood sample is a very low-risk procedure. In some cases, you may have slight bruising at the site where the blood sample was taken.

Vitamin B12 Test Results

Receiving test results

Your health care provider may share your vitamin B12 test results with you, or you may be able to access results through an online portal. Vitamin B12 results are typically available within a few business days.

Interpreting test results

Your test report will indicate your blood level of vitamin B12, as well as the laboratory’s reference range. Reference ranges are the test result ranges that are considered normal.

Reference ranges can vary slightly, depending on the laboratory used. A normal vitamin B12 level generally falls between 200 to 800 picograms per milliliter (pg/mL).

If your result is between 200 and 300 pg/mL, your result is considered borderline, and your doctor may have you retake the vitamin B12 test or undergo additional testing.

Values under 200 pg/mL indicate a vitamin B12 deficiency. Vitamin B12 deficiency may be due to known causes such as a vegan diet, medications, problems with the pancreas, or surgery or diseases affecting the digestive system. Deficiency may also be a result of:

  • Inability to produce intrinsic factor: Intrinsic factor is normally secreted by the cells of the stomach. An inability to produce this protein may be caused by weakening of the stomach lining or an autoimmune condition and leads to a condition called pernicious anemia.
  • Overgrowth of bacteria or fish tapeworm infestation in the digestive system: In these disorders, bacteria or parasites consume vitamin B12 and leave less for the infected person to absorb.
  • Poor absorption of vitamin B12 due to low stomach acid: Low stomach acid can be due to age, diseases that cause low stomach acid, or the use of drugs to decrease stomach acidity.
  • Other autoimmune problems: These can include thyroid disease or vitiligo.

Higher vitamin B12 levels are uncommon since excess vitamin B12 is usually removed in the urine. However, some conditions can cause an increase in vitamin B12 levels, including liver diseases and myeloproliferative disorders, which are diseases that affect the production of blood cells.

Are test results accurate?

Your health care provider is likely to take a number of factors into consideration when interpreting your test results and determining whether follow-up testing is appropriate.

First, research has shown that there is variation in an individual’s vitamin B12 levels over a period of weeks and that some people experience significant fluctuations. Further testing may be needed if your vitamin B12 levels are in the borderline range or if the results of your laboratory testing don’t match up with your symptoms or a previous diagnosis.

In addition, certain factors may interfere with the accuracy of your test results.

A false positive means it looks as if a deficiency is present when that is not actually the case.

Factors which increase the risk of a false positive for a vitamin B12 deficiency include:

  • Multiple myeloma, a cancer of certain white blood cells
  • HIV infection
  • Pregnancy
  • Use of oral contraception
  • Use of the anticonvulsant drug phenytoin

Other factors may cause your vitamin B12 levels to appear higher than they are. This can mask a deficiency and cause a false negative, making it appear that no deficiency is present when you actually have one:

  • Blood disorders like chronic myelogenous leukemia or polycythemia vera
  • Alcoholic liver disease, cirrhosis, or hepatitis
  • Kidney disease
  • Use of nitrous oxide, also known as laughing gas or whippets
  • Autoimmune disorders
  • Rare genetic disorders

If the accuracy of your vitamin B12 level is uncertain, you may be asked to take additional tests.

Do I need follow-up tests?

You may need follow-up tests if your doctor wants to confirm the accuracy of your test results, if your vitamin B12 level is borderline, or to further investigate a vitamin B12 deficiency.

If your vitamin B12 test result is borderline, meaning between 200 and 300 pg/mL, you may need additional testing. Alternatively if your test results appear normal but your doctor suspects that your symptoms are related to a B12 deficiency, the following tests may be ordered:

If your vitamin B12 test shows a deficiency, you may have additional tests to determine the underlying cause. Understanding the cause of your vitamin B12 deficiency will help your health care provider choose the most suitable treatment for you.

You may have a known risk factor, like celiac disease, pancreatic problems, or another digestive disease that makes it hard to absorb nutrients from your food. If no underlying cause is known, the tests chosen to detect the underlying cause of your deficiency will depend on your medical history and symptoms.

To see if vitamin B12 deficiency is due to an autoimmune disorder affecting intrinsic factor, an intrinsic factor antibody test may be performed.

Questions for your doctor about test results

It may be helpful to ask your doctor, nurse, or physician’s assistant the following questions:

  • Was my vitamin B12 level normal?
  • Do you believe my vitamin B12 level is accurate, or are more tests needed to confirm it?
  • If low, will I need additional testing to understand the cause of the deficiency?
  • If low, what treatment approach do you recommend to correct my vitamin B12 deficiency?

Related Tests

Vitamin B12 test vs. folate test

Both vitamin B12 and folate deficiencies can cause megaloblastic anemia. Vitamin B12 and folate testing are often ordered together when signs of megaloblastic anemia are seen on other tests, such as blood count tests or blood smear tests.

Some people have vitamin B12 and folate deficiencies at the same time, while others have low levels of only one nutrient. Some of the risk factors that increase the likelihood of  a vitamin B12 deficiency also increase the likelihood of a folate deficiency. However, other types of risk factors only increase the chances of developing a deficiency of one of these two nutrients.

A doctor will assess a person’s health history and risk factors like age, diet, and use of certain medications when deciding whether to order vitamin B12 or folate tests together or separately.

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