In layman’s terms, the morphology of red blood cells is what they look like. In clinical practice, it is often possible to make a diagnosis of many diseases by morphological examination of red blood cells, because normal human red blood cells appear as a double-sided concave disc shape with a diameter of about 7.5 μm and a volume of between 80-100 fL. If the red blood cell morphology is small, with a diameter of less than 7.5 μm and a volume of less than 80 fL, this is microcytic anemia, and the most common diseases are iron deficiency anemia or thalassemia, so that it can provide useful help in clinical diagnosis. If the morphology of the red blood cells is huge, with an average volume of more than 100 fL, this condition is megaloblastic anemia, mostly caused by folic acid or vitamin B12 deficiency. If there is a significant increase in the number of spherical red blood cells in the peripheral blood, the most common disorder is hereditary spherocytosis.