The most common blood test is the routine blood test. To understand the routine blood test, first of all, it is necessary to clarify what kinds of blood cells are present in the blood and what are the normal values of these blood cells. In addition, if there is an increase or decrease in the value, respectively, what does it mean. For example, in the routine blood test: the first item is the number of white blood cells, which has a normal range. The increase in the number of white blood cells is common in various inflammatory diseases, or when the human body suffers from severe injuries, the number of white blood cells will increase. Patients with acute leukemia or chronic leukemia may have an abnormally high white blood cell count. After looking at the white blood cells, we must also look at the red blood cell count, which is lower than the normal range, most commonly in various types of anemia, including iron deficiency anemia, aplastic anemia, and hemolytic anemia. And the lower the number of red blood cells, the lower the hemoglobin concentration, representing the more severe anemia. Finally, we also have to look at the platelet count. If the platelet count is below the normal range, it is thrombocytopenia. If the platelet count is outside the normal range, it is seen as reactive thrombocytosis or primary thrombocytosis.