<prompt> Which of the following is most likely to cause of non Megaloblastic macrocytic anemiaVitamin B12 deficiencyHypothyroidismThiamine deficiencyFolic acid deficiency  <response>: 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 . 