Which of the following parameters will fall the earliest in iron deficiency

MCV is reduced in iron defeciency while a high value indicates macrocytic anaemia The first red cell index to become abnormal is MCV But it maynot be found always even in established iron defeciency as the increased drive to erythropoiesis results in large propoion of young large cells A typical iron deficiency anemia shows the following blood values: Hemoglobin--less than 10 gm% Red blood cells --less than 4 million/mm3 PCV--less than 30% MCHC -- less than 30% MCV -- less than 75 u3 MCH--less than 25 pg Reference: Textbook of Obstetrics,Sheila Balakrishn; 2nd edition; Pgno:285