Mean corpuscular volume (MCV) gives us a measure of red cell size; reduced MCV indicates microcytosis suggestive of iron deficiency and increased MCV is suggestive of megaloblastic anemi
Red cell distribution width (RDW): A high value indicates the degree of anisocytosis which is often a marker of nutritional anemia. Iron deficiency being a nutritional anemia would show cells of different sizes (small and normal sized red cells) thus increasing RDW. Thalassemia trait is a genetic condition where all red cells produced from the bone marrow are uniformly small. Thus in patients with low MCV along with normal RDW, thalassemia trait should be ruled out.
Peripheral smear: A good peripheral smear gives us clues to the etiology of anemia as well as information about the other cell lines.
Hemoglobin electrophoresis to rule out hemoglobinopathies if indicated.