This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood, Subject name: Medicine
[{'content': 'A 69-year-old woman, with poor dietary habits and alcoholism, is found to have a macrocytic anemia with hyper segmented neutrophils. Which of the following is the most appropriate diagnostic test? \nSelect and explain. \nA. red blood cell vitamin levels, B. plasma vitamin levels, C. bone marrow, D. Schilling test', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Folate deficiency can be secondary to small bowel disease, alcoholism, inadequate intake, disease states with high cell turnover (hemolytic anemia), drugs (methotrexate), and pregnancy. The concentration of folate in plasma changes rapidly with changes in food intake, so the diagnosis of anemia secondary to folate deficiency is made more reliable by measuring red blood cell folate.', 'role': 'assistant'}]