 RBCs often appear hypochromic (paler than usual) and microcytic (smaller than usual) when viewed with a microscope.The Mentzer index (mean cell volume divided by the RBC count) predicts whether microcytic anemia may be due to iron deficiency or thalassemia, although it requires confirmation.Macrocytic anemia can be further divided into "megaloblastic anemia" or "nonmegaloblastic macrocytic anemia".