Test Quick Guide

Vitamin B12 testing measures the level of that vitamin 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 many 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 diagnose a possible deficiency and recommend appropriate treatment.

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 to diagnose or monitor certain health problems.

Your doctor might order a vitamin B12 test if you show symptoms of anemia or issues with the nervous system like mental changes, weakness, loss of balance or numbness, pain, and tingling in the arms and legs. A vitamin B12 test can also be ordered as a follow-up if you had an abnormal blood test that suggests megaloblastic anemia, when red blood cells are unusually large and do not function properly.

What does the test measure?

The test measures your vitamin B12 levels, which are important for many aspects of 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 in all of our cells.

When should I get this test?

Up to 15% of people in the U.S. have a vitamin B12 deficiency. 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 vitamin B12 deficiency due to age or preexisting health conditions. They may undergo regular vitamin B12 testing to check whether their levels are normal.

Anemia is one factor related to inadequate vitamin B12, with symptoms including fatigue, difficulty concentrating, pale skin, shortness of breath, diarrhea, nausea, and loss of appetite. With anemia, your body doesn’t have enough healthy red blood cells to carry oxygen to tissues.

A vitamin B12 deficiency can lead to a type of anemia known as megaloblastic anemia. Megaloblasts may be detected through routine blood testing before you develop symptoms of anemia. When this happens, follow-up testing is typically performed, including a vitamin B12 test.

Nervous system symptoms are another trigger for vitamin B12 testing. Common symptoms include neuropathy, weakness, poor balance, confusion, and dementia.

And you might have risk factors associated with a vitamin B12 deficiency, including age (75 years or older), lack of protein in the diet, medications that interfere with vitamin B12 absorption like histamine blockers, or decreased absorption of vitamin B12 because of a stomach disease like celiac, cancer, or pancreatic insufficiency.

People more likely to experience low vitamin B12 levels include older adults, children, vegans and vegetarians, diabetics, those who have had gastric bypass surgery, women who are breastfeeding, and if you have a condition that can impact absorption like Crohn’s disease.

Your doctor can best assess the nuances involved in determining whether you should get vitamin B12 testing because many of these symptoms overlap with other health conditions and could require different types of screening.

Finding a Vitamin B12 Test

How can I get a vitamin B12 test?

Vitamin B12 testing is most often performed at a doctor’s office or another medical setting like a laboratory or hospital. A doctor normally prescribes vitamin B12 tests, but they may be available without a doctor’s order at a walk-in lab or an at-home test kit.

You can order a vitamin B12 test online. While you do not need a doctor’s order to get the kit, discussing the results with your physician is important.

Can I take the test at home?

Several commercially available test kits 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, and there are at-home micronutrient test kits that include B12 in the panel.

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. After a few days, your test results are available via a secure online platform.

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

If an at-home test detects an abnormal vitamin B12 level, your doctor will likely 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 testing for B12 depends on how comprehensive the panel is, where the test is conducted, and whether your insurance plan will cover vitamin B12 testing. Keep in mind copays and deductibles that may apply. Be sure to refer to the lab, your doctor, and health plan for specific vitamin B12 testing cost details.

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. If you choose an at-home kit that screens for vitamin B12, you will receive the necessary supplies to take your blood sample. Some micronutrient at-home tests might screen for B12 and other vitamins through a urine or hair sample.

Before the test

Before taking a vitamin B12 test, it is important to fast for six to eight 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, 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 conducted in a lab or health care setting, a small blood sample 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. Otherwise, you can resume everyday activities.

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. If you order an at-home test kit, you’ll ship the sample to a participating lab and receive results within a few days of them receiving your specimen.

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. Keep in mind 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 less than 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, surgery, or diseases affecting the digestive system. Deficiency may also result from:

  • Inability to produce intrinsic factor: This protein is normally secreted by the cells of the stomach. An inability to produce this may be caused by the weakening of the stomach lining or an autoimmune condition that 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. But some conditions can cause an increase in vitamin B12 levels, including liver diseases and myeloproliferative disorders that affect the production of blood cells.

Your health care provider is likely to consider many factors when interpreting your test results and determining whether follow-up testing is appropriate First, research has shown that there is variation in vitamin B12 levels over weeks and that some people experience significant fluctuations. In addition, certain factors may interfere with the accuracy of your test results.

For example, factors that 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

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.

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

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?

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