Serum or plasma mass concentration of vitamin B12 (cobalamin)

Why Is This Test Done?

Your doctor may order this test if you have symptoms like fatigue, weakness, numbness, or tingling in your hands and feet. It can also be part of screening for pernicious anemia, certain gastrointestinal disorders, or malabsorption issues. Additionally, it may be checked during pregnancy, especially if you have risk factors for deficiency.

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 blood draw if instructed by your healthcare provider. Bring any medications you’re currently taking, as some (like certain antacids or proton pump inhibitors) can affect results.

What Happens During the Test?

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it usually takes only a few minutes. The blood sample will be sent to a lab for analysis.

What Are Possible Results?

Results are compared to standard ranges, but exact values can vary by lab. Low levels may signal vitamin B12 deficiency, while very high levels could indicate conditions like certain cancers or kidney disease. Your doctor will interpret results in the context of your symptoms and medical history.