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: Medicine
During the course of evaluation of a case of polycythemia following investigation may be required to establish the cause EXCEPT - 
Select and explain. 
A. Ervthropoietin level, B. Aerial blood gas analysis, C. Bone marrow examination, D. Serum iron profile
D: Serum iron profile
Answer: D: Serum iron profile 
Explanation: <p>In secondary polycythemia,erythropoietin levels are raised. Bone marrow examination shows erythroid hyperplasia . Aerial blood gas analysis to look for oxygen saturation .</p><p>Reference :Harsh mohan textbook of pathologysixth edition pg no 359.</p>