The diameter of red blood cells in normal human peripheral blood is around 7.5 μm, and the volume of red blood cells is between 80-100 fL. If the volume of red blood cells is lower than 80 fL, it is small in size, which is clinically called microcytic red blood cells. Small red blood cell volume can be seen in a variety of diseases, the most common diseases are two, the first, iron deficiency anemia, iron deficiency anemia due to iron deficiency, red blood cells can not be normal synthesis of hemoglobin, each red blood cell hemoglobin content is reduced, resulting in small red blood cell volume, the situation of low red blood cell volume, after giving iron supplementation treatment, the red blood cell hemoglobin content increased, the red blood cell volume will The volume of red blood cells will gradually increase. Secondly, thalassemia, due to the impaired synthesis of peptide chains, cannot synthesize hemoglobin normally, which will also lead to low red blood cell volume, but thalassemia is a hereditary disease, so blood supplementation cannot change the low red blood cell volume.