<prompt> During the course of evaluation of a case of polycythemia following investigation may be required to establish the cause EXCEPT -Ervthropoietin levelAerial blood gas analysisBone marrow examinationSerum iron profile  <response>: In secondary polycythemia,erythropoietin levels are raised. Bone marrow examination shows erythroid hyperplasia . Aerial blood gas analysis to look for oxygen saturation .Reference :Harsh mohan textbook of pathologysixth edition pg no 359. 