This test measures both vitamin B12 and folate levels in the blood, which are essential nutrients for red blood cell formation and nervous system function. Vitamin B12 and folate deficiencies can cause megaloblastic anemia, characterized by large, immature red blood cells. Vitamin B12 deficiency can also lead to neurological problems including numbness, tingling, and cognitive issues. This test is commonly ordered when patients have symptoms of anemia, neurological symptoms, or when monitoring treatment for these deficiencies. It's particularly important for vegetarians, older adults, and those with gastrointestinal conditions that may affect absorption. Early detection and treatment of these deficiencies can prevent serious complications.