Introduction Red blood cell (RBC) indices describes RBC size and shape, as well as hemoglobin content plays an important role in determining the cause of anemia RBC indices include mean corpuscular volume (MCV) mean corpuscular hemoglobin (MCH) mean corpuscular hemoglobin concentration (MCHC) Mean Corpuscular Volume Reflects average RBC volume Anemia classification microcytic (< 80 fL) normocytic (80 μm - 100 fL) macrocytic (> 100 fL) Mean Corpuscular Hemoglobin Reflects average hemoglobin content low hemoglobin content results in a low MCH hypochromia on peripheral blood smear e.g., iron deficiency anemia and thalassemias Mean Corpuscular Hemoglobin Concentration (MCHC) Reflects average hemoglobin concentration of RBCs elevated MCHC RBC agglutination spherocytosis sickle cell anemia hemoglobin C disease decreased MCHC in conditions of decreased hemoglobin production Red Cell Distribution Width Reflects variation in size of RBCs elevated RDW implies a high degree of RBC size variation iron deficiency anemia myelodysplastic syndromes hemoglobinopathies low RDW implies a more homogenous RBC size