What’s a Vitamin B12 Test?

Medically Reviewed by Sabrina Felson, MD on May 29, 2023
3 min read

Vitamin B12 is vital for good health. Your body needs steady levels of this nutrient to make enough red blood cells and keep your nervous system working.

For most people who eat a balanced diet, low B12 levels are rare. But there are reasons why they may dip below normal. A simple blood test can show whether your levels are healthy, low or somewhere in between.

Your doctor may recommend you have one for a few different reasons, such as:

  • You’ve been diagnosed with anemia.
  • They suspect you have a medical condition that affects how well your body absorbs B12.
  • You’re taking medications that may interfere with B12 absorption.
  • You have symptoms linked to low B12 levels.
  • You follow a vegan or strict vegetarian diet.

The main health problem associated with poor B12 absorption is a condition doctors call “pernicious anemia.” It develops if you lack intrinsic factor, a type of protein made in the stomach. Without it, you can’t absorb enough vitamin B12 from food.

Crohn’s disease and celiac disease may also cause your B12 levels to go down.

Several types of medications might affect your vitamin B12 levels. Among the most common are drugs to help treat gastroesophageal reflux disease (GERD). Medications called proton-pump inhibitors reduce the amount of acid in the stomach, which is needed for food to release B12.

If you’re not taking any of these medications or haven’t been diagnosed with pernicious anemia or other health problems that might cause lower B12 levels, your doctor may order the test based on your symptoms and dietary or health history.

Common symptoms of low vitamin B12 include:

  • Fatigue
  • Fuzzy thinking
  • Numbness or tingling in your hands and feet
  • Headaches
  • Moodiness

These could be signs of many conditions. A blood test that checks your B12 levels can rule out or confirm that your low B12 levels may be the issue.

It’s a simple blood test. You can get it anytime, and you don’t need to go without food (fasting) before you do. Your doctor can add it to the order for your blood test that checks your levels of cholesterol, glucose, and other markers of health.

You should tell your doctor about all of the medications and supplements you take before the test. Some of them may affect the results.

The normal range for vitamin B12 can vary slightly depending on the lab. But a normal level of vitamin B12 in your bloodstream is generally between 190 and 950 picograms per milliliter (pg/mL). Between 200 to 300 pg/mL is considered borderline and your doctor may do more testing. Below 200 pg/mL is low and more testing is needed.

In some cases, your doctor may also test for your folate level because low folate can cause signs and symptoms similar to low B12.

If your vitamin B12 test shows that your levels are healthy, you don’t need to do anything but continue eating a balanced diet. Sources of vitamin B12 include fish, meat, dairy, and other foods fortified with B12, like cereal and milk.

If you’re still concerned about your levels, talk with your doctor about whether B12 supplements or dietary changes make sense.

But if you have low vitamin B12 levels, you'll likely need to supplement your B12 with injections or oral supplements depending on your stomach's ability to absorb the vitamin.

Vitamin B12 deficiency can lead to problems with brain function, your nervous system, and other aspects of your health. It’s important to check your levels if there are any signs that they are low.

Older adults are at increased risk for low levels of vitamin B12. Talk to your doctor about whether your diet provides enough B12, or if taking a supplement would help.