This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc. (R.B.C), Subject name: Pathology
A man presents with fatigue. Hemogram analysis done suggested low Hb, high MCV. The next investigation is? 
Select and explain. 
A. Vit B12/folatelevels, B. Bone Marrow, C. S. Iron studies, D. Reticulocyte count
D: Reticulocyte count
Answer: D: Reticulocyte count 
Explanation: 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.