This Vitamin B12 blood test measures the level of vitamin B12 in the blood to determine if it is deficient. It is important to monitor levels of this vitamin, as low levels can cause anemia, fatigue, nerve damage, and other health issues. The test can also help diagnose conditions such as pernicious anemia and deficiency syndromes. The results can be used to determine if dietary changes, supplements, or other treatments are needed to maintain optimal health.