Serum or plasma concentration of vitamin B12 (cobalamin)

Why This Test Is Done

Doctors may order a vitamin B12 test if you have symptoms like fatigue, numbness, weakness, or trouble concentrating. It’s also used to check for pernicious anemia, nerve damage, or other conditions linked to low vitamin B12 levels. Sometimes, it’s part of routine blood work for older adults or those with certain dietary restrictions.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it’s part of a broader blood workup. Bring any medications you’re taking, as some (like certain blood thinners) can affect results.

What the Results Mean

Low levels may indicate vitamin B12 deficiency, which can be caused by poor diet, absorption issues (like in pernicious anemia), or conditions like Crohn’s disease. High levels alone are less common but could signal liver disease or other metabolic issues. Your doctor will interpret results in the context of your symptoms and overall health.

Common Conditions Linked to Vitamin B12

Deficiency can lead to anemia (fewer healthy red blood cells), neurological problems (like tingling or balance issues), or cognitive changes. Early diagnosis and treatment (often with vitamin B12 injections or supplements) can prevent long-term damage.