Serum or Plasma Vitamin B12 (Cobalamin) Concentration

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 could also be done to check for vitamin deficiencies, especially if you have conditions like pernicious anemia, celiac disease, or poor diet. Sometimes, it’s part of a routine checkup for older adults or those with certain gastrointestinal disorders.

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 your blood is drawn from a vein. If you’re tested for urine or saliva, follow any specific instructions your doctor provides. Avoid taking vitamin supplements or certain medications that might affect results for 24 hours before testing.

How the Test Is Performed

A healthcare provider will draw blood from a vein in your arm using a small needle. The blood sample is sent to a lab for analysis. If testing urine or saliva, you’ll provide a sample directly to the lab. The lab will measure the concentration of vitamin B12 in your sample using a specialized immunoassay or other sensitive methods.

What the Results Mean

Low levels of vitamin B12 can indicate deficiencies caused by poor absorption (e.g., due to conditions like atrophic gastritis or malabsorption), dietary restrictions, or certain medications. High levels may be seen in some genetic disorders or during pregnancy. Your doctor will interpret the results in the context of your symptoms and medical history.