Test Details: This test is used as a screening tool to confirm various infections, to detect an unsuspected hematologic disorder, or to monitor effects of radiation or chemotherapy. RBCs, WBCs and platelets are produced in the bone marrow and released into the peripheral blood. The primary function of the RBC is to deliver oxygen to tissues. WBCs are key components of the immune system. Platelets play a vital role in blood clotting. Mean corpuscular volume (MCV) is a measure of the size of the average RBC. Anemias are characterized as microcytic (MCV <80), macrocytic (MCV >100), or normocytic. The red cell distribution width (RDW) is a measure of the degree of variation in RBC size (Anisocytosis) and the shape of RBC (Poikilocytosis). RDW may be helpful in distinguishing between some anemias. For example, iron deficiency anemia is characterized by a high RDW, while thalassemia is characterized by a low RDW. Complete blood counts are used as clinical guides in the diagnosis or monitoring of several diseases.