Serum or plasma concentration of a substance related to vitamin B12 metabolism (likely holotranscobalamin II or total holotranscobalamin)

Why This Test Is Done

Your doctor may order this test if you have symptoms like fatigue, numbness, or tingling in your hands and feet, or if you have risk factors for vitamin B12 deficiency, such as poor diet, pernicious anemia, or certain medications that interfere with absorption.

What to Expect Before the Test

No special preparation is needed. You’ll have a small needle inserted into your arm or hand to draw blood. It usually takes about 15 minutes. If you’re taking medications that affect vitamin B12 levels, let your doctor know.

What the Test Results Mean

Low levels may indicate vitamin B12 deficiency, which can cause nerve damage or anemia. High levels might suggest overabsorption or certain medical conditions. Your doctor will interpret results in the context of your symptoms and other tests.

Common Causes of Abnormal Results

Deficiency can result from poor diet, malabsorption issues (like celiac disease or atrophic gastritis), certain medications, or conditions like pernicious anemia. Overabsorption may occur in rare genetic disorders or with excessive vitamin B12 supplements.