What a B12 test shows

A B12 test measures the amount of vitamin B12 in your blood. Your doctor orders it when you report symptoms like fatigue, weakness, tingling in your hands or feet, or memory problems — all of which can signal B12 deficiency. The test itself is a straightforward blood draw, usually done at a lab or your doctor's office.

B12 is a vitamin your body needs to make red blood cells and keep your nervous system working. You get it from animal products like meat, fish, eggs, and dairy. Some people's bodies cannot absorb B12 properly even when they eat enough of it, which is why a blood test matters — it tells your doctor whether your levels are low and whether you need treatment.

The test result comes back as a number, measured in picograms per milliliter (pg/mL). What counts as "low" varies slightly between labs, but most consider anything below 200 pg/mL a sign of deficiency. Your doctor will interpret your specific result in the context of your symptoms and medical history.

Key Takeaways

  • A B12 blood test measures whether you have enough B12 to support red blood cell production and nerve function.
  • Symptoms that prompt a B12 test include fatigue, weakness, tingling in extremities, and cognitive changes, though some people have low B12 without noticing symptoms.
  • Results below 200 pg/mL typically indicate deficiency, but your doctor interprets the number alongside your symptoms and diet history.
  • If your test shows low B12, your doctor may order a follow-up test to determine whether the problem is absorption or dietary intake.

Why doctors order B12 tests for older adults

B12 deficiency becomes more common as you age. After 50, your stomach produces less acid, which your body needs to separate B12 from food. This means you can eat enough B12 but still not absorb it. Additionally, some medications that older adults take regularly — particularly metformin for diabetes and proton pump inhibitors for acid reflux — interfere with B12 absorption.

Older adults are also more likely to follow vegetarian or vegan diets, or to have conditions like pernicious anemia (an autoimmune disorder that prevents B12 absorption) or digestive disorders such as Crohn's disease or celiac disease. Any of these situations can lower B12 levels enough to cause problems.

The symptoms of B12 deficiency can mimic other conditions common in older age — memory loss, confusion, or balance problems might be attributed to normal aging or early dementia when B12 deficiency is actually the cause. A B12 test can rule out deficiency as a culprit and point toward the real problem.

What happens before and during the test

You do not need to fast or prepare in any special way for a B12 test. You can eat and drink normally before your appointment. The test itself takes only a few minutes: a lab technician or nurse draws a small amount of blood from a vein in your arm, usually the inside of your elbow. You may feel a brief pinch, and some people experience mild bruising afterward.

Tell your doctor or the lab technician if you take any medications or supplements before the test, particularly if you are already taking B12 injections or high-dose B12 supplements. These can affect your result. If you have recently received a B12 injection, let them know the date — you may need to wait a few days before the test to get an accurate reading of your baseline level.

The blood sample is sent to a lab for analysis. Results typically come back within a few days to a week. Your doctor's office will contact you with the result and discuss what it means for your health.

Understanding your test results

Most labs use a reference range of 200 to 900 pg/mL as normal. If your result falls within that range, your B12 level is adequate. If it is below 200, your doctor will likely discuss treatment options with you. Some doctors also consider levels between 200 and 300 as borderline low, especially if you have symptoms.

A low result does not automatically mean you need treatment — your doctor will also consider your symptoms, your diet, and whether you have conditions or take medications that affect B12 absorption. If you have no symptoms and your level is only slightly low, your doctor might recommend dietary changes or monitoring rather than injections.

If your test is low and your doctor suspects an absorption problem rather than a dietary shortage, they may order a second test called the Schilling test or methylmalonic acid test. These tests help determine whether your body is failing to absorb B12 from food or whether you straightforward are not eating enough of it. The answer changes the treatment plan.

Treatment options if your B12 is low

If your test shows deficiency and you have symptoms, your doctor typically recommends B12 injections. These bypass your digestive system and deliver B12 directly into your muscle, which works even if your body cannot absorb it from food. Injections are usually given monthly, though some people need them more or less frequently depending on their condition.

Oral B12 supplements are an option if your deficiency is caused by diet rather than absorption problems. These come as tablets, lozenges, or liquids and are available over the counter. However, if your body cannot absorb B12 properly, oral supplements often do not work well enough.

If your deficiency is caused by a medication you take, your doctor might adjust your dose, switch you to a different medication, or recommend B12 supplementation alongside your current treatment. The goal is to bring your B12 level back to normal and resolve your symptoms.

Who should consider a B12 test

You may want to discuss a B12 test with your doctor if you experience unexplained fatigue, weakness, tingling or numbness in your hands or feet, balance problems, memory loss, or mood changes. You should also mention it if you follow a vegetarian or vegan diet, take metformin or proton pump inhibitors regularly, or have a digestive disorder.

Some doctors recommend routine B12 screening for all adults over 50, while others only test when symptoms appear. This varies by practice and by your individual health history. If you are unsure whether a B12 test makes sense for you, ask your doctor at your next visit.

If you have already been diagnosed with B12 deficiency and are receiving treatment, your doctor will order periodic tests to make sure your level stays in a healthy range and your symptoms improve.

Cost and insurance coverage

A B12 blood test typically costs between $30 and $100 if you pay out of pocket, though the price varies by lab and location. Most insurance plans cover the test when your doctor orders it for a medical reason — such as symptoms of deficiency or a condition known to affect B12 absorption. Medicare covers B12 testing as part of routine preventive care and diagnostic workups.

If cost is a concern, ask your doctor's office what the test will cost under your insurance plan before you have it done. Some community health centers and urgent care clinics offer B12 testing at lower cost than hospital labs. You can also call ahead to different labs in your area and compare prices.

Frequently Asked Questions

How long does it take to get B12 test results?

Most labs return results within three to seven business days. Your doctor's office will contact you once the result is ready. If you need results urgently, ask your doctor whether the lab can prioritize your sample or whether results can be delivered electronically to speed up the process.

Can I take B12 supplements before my test?

If you are already taking B12 supplements or injections, tell your doctor before the test. Recent supplementation can raise your blood level artificially and give a false picture of your baseline. Your doctor may ask you to stop supplements for a period before testing, or they may interpret your result with that information in mind.

What if my B12 is low but I have no symptoms?

Some people have low B12 without noticing symptoms, especially if the deficiency is mild or has developed slowly. Your doctor may still recommend treatment to prevent symptoms from developing later, or they may suggest monitoring your level with repeat tests over time. The decision depends on how low your level is and what is causing the deficiency.

Is a B12 test the same as a complete blood count?

No. A complete blood count (CBC) measures red blood cells, white blood cells, and platelets but does not measure B12 levels. A B12 test is a separate blood test that specifically measures B12 concentration. Your doctor may order both tests if they suspect anemia, since B12 deficiency can cause anemia.

Can I get a B12 test without seeing my doctor first?

Some labs offer direct testing without a doctor's order, though your insurance may not cover the cost if there is no medical reason documented. You can contact a local lab to ask about their policy. However, having your doctor order the test ensures the result is interpreted in the context of your symptoms and medical history, which leads to better decisions about treatment.