Vitamin B12 (Serum or Plasma Concentration)

Your doctor may order this test if you have symptoms such as ongoing tiredness, weakness, pale skin, numbness or tingling in your hands and feet, balance problems, or memory difficulties. The test may also be recommended if you follow a vegan or vegetarian diet, have a condition that affects nutrient absorption, take certain long-term medications, or have a family history of pernicious anemia.

Doctors may order a vitamin B12 test if you have symptoms like fatigue, numbness or tingling in your hands and feet, weakness, balance problems, memory issues, or unexplained anemia. It may also be checked during routine blood work, especially if you have conditions like pernicious anemia, celiac disease, or vegetarian/vegan diets that can lead to low vitamin B12 levels.

In most cases, no special preparation is needed for a vitamin B12 blood test, but your doctor will let you know if you should avoid eating or drinking for several hours beforehand. Tell your care team about all prescription drugs, vitamins, and supplements you take, since some can affect the results. The test is done with a simple blood draw, usually from a vein in your arm, and it typically takes only a few minutes.

No special preparation is needed for this blood test. You may have a small needle inserted into your arm or hand to draw a blood sample. If you’re on certain medications, let your healthcare provider know as they may affect results.

Your results are compared with a reference range, and normal values can vary slightly from one laboratory to another. A low result may point to a vitamin B12 deficiency, which can affect your blood, nerves, and energy levels. A result within the normal range usually means your body is getting and absorbing enough B12. Your doctor will interpret your numbers together with your symptoms and may order follow-up tests to identify the underlying cause.

Low vitamin B12 levels may indicate deficiency, which can cause nerve damage or anemia. High levels are less common but could suggest certain medical conditions or medications. Your doctor will interpret results in the context of your symptoms and overall health.

Low vitamin B12 levels can develop for several reasons. Common causes include pernicious anemia, an autoimmune condition that blocks absorption; diets low in animal products, such as vegan or vegetarian eating patterns; digestive conditions like celiac disease or Crohn's disease; stomach or weight loss surgery; and long-term use of medications such as metformin or proton pump inhibitors. Being over age 60 also raises the risk because the body absorbs B12 less efficiently over time.

Deficiencies can stem from poor diet (especially in vegans/vegetarians), conditions like pernicious anemia (which impairs vitamin B12 absorption), or digestive disorders like Crohn’s disease or celiac disease. Medications like proton pump inhibitors may also reduce absorption.