A Vitamin B12 test measures the level of vitamin B12 in your blood, an essential nutrient needed for red blood cell production, nerve function, and DNA synthesis. Low B12 levels can lead to fatigue, weakness, numbness, memory issues, mood changes, and certain types of anemia, especially pernicious anemia. Doctors usually recommend this test when symptoms of deficiency appear or if you follow a vegetarian/vegan diet, as B12 is mostly found in animal-based foods.

For the Vitamin B12 test, a small blood sample is collected from a vein, and fasting for 6–8 hours may be recommended for more accurate results. This test helps diagnose deficiencies, monitor treatment response, and evaluate overall nutritional status. It is often done along with Folate, Hemoglobin, and other related tests for a complete evaluation.