Ans. (d) Reticulocyte count(Ref: Robbins 9th/pg 645-648)This is a tricky question as the initial investigation looks like B12 /folate levels, as the patient has macrocytosis.But remember, Macrocytosis can also be seen in hemolytic anemia, as newer RBC precursors released are larger in size.So the initial investigation should be reticulocyte countIf reticulocyte % is low it can be macrocytic anemia & if there is reticulocytosis, then it can be a case of hemolytic anemia.