Red blood cells (RBCs) or red blood corpuscles are the most common type of blood cells responsible for delivering oxygen (O2) to the body tissues via blood flow through the circulatory system. RBCs are also called as erythrocytes, haematids or erythroid cells. RBC histogram are good indicators of the range, size, shape, and other prominent features of the red cell morphology. RBC histogram is basically depiction of RBC distribution and is dependent on MCV and RDW values. In case of abnormal RBC distribution there will be a flag and review may be required based on abnormal MCV or RDW values. Another method for assurance of these flags is smear examination for RBC morphology. MCV stands for the average size of red blood cells (erythrocytes) in a blood sample and is used and interpreted along with blood counts and other RBC indices such as - MCHC AND RDW for better understating of the lying condition.The value of MCV is of great implication even when the RBC count and other examinations are normal especially in kidney disease. Low range of MCV is indicative of small red blood cells and termed as microcytosis while high MCV is indicative of larger RBCs in blood and is called as macrocytosis.