This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Anatomy
Which of the following is most likely to cause of non Megaloblastic macrocytic anemia 
Select and explain. 
A. Vitamin B12 deficiency, B. Hypothyroidism, C. Thiamine deficiency, D. Folic acid deficiency
B: Hypothyroidism
Answer: B: Hypothyroidism 
Explanation: Ref Harrison 19 th ed pg 640 marrow is usually hypercellular and the anemia is based on ineffective erythropoiesis. The cause is usually a deficiency of either cobalamin (vitamin B12) or folate, but megaloblas- tic anemia may occur because of genetic or acquired abnormalities that affect the metabolism of these vitamins or because of defects in DNA synthesis not related to cobalamin or folate .