Once a child is seen, the most common test requested by the doctor is the peripheral blood test, in which a very small amount of blood is taken from the child’s fingertips, or earlobes, or heels for testing, and the report can be seen after a few moments, also known as capillary blood collection. The following items are included in the routine blood report: 1. white blood cell count and white blood cell classification. The normal white blood cell count in children is 0.5 to 1.2×109/liter. In newborns 2 weeks after birth, the white blood cell count can be as high as about 1.2×109/l. The average white blood cell count in children 6 months to 6 years old is 1.0×109/l, and after 6 years old, it is generally normal at 0.7 to 0.8×109/l. The white blood cell count may increase when the pediatrician has an acute bacterial infection, leukemia, and after surgery. When suffering from typhoid fever, rubella, aplastic anemia and certain acute leukemias, the white blood cell count may be reduced. In infants after 6 months of age, lymphocytes predominate, accounting for about 69% of the cells and neutrophils for about 30%. In preschool children, neutrophils gradually increase and lymphocytes gradually decrease, and the two can be equal around 6 years of age; after 6 years of age, neutrophils gradually dominate, and after 8 years of age, neutrophils account for about 60% and lymphocytes for about 30%. Increased neutrophils are seen in acute bacterial infections, after surgery or injury; decreased neutrophils are seen in typhoid fever, influenza, aplastic anemia, etc. Increased lymphocytes are seen in whooping cough, rubella, lymphocytic leukemia; decreased lymphocytes are seen in the acute phase of certain infectious diseases, excessive radiation exposure, etc. 2.Red blood cell count and hemoglobin measurement. Normal pediatric erythrocytes are often maintained above 5×1012/liter and hemoglobin is above 110 g/liter (above l20 g/liter after 6 years of age). When hemoglobin is below these standards, it is considered anemia. Increased hemoglobin and erythrocytes are most often seen in dehydration, cyanotic congenital heart disease, erythrocytosis, etc. Decreased both are often seen in children with anemia. In leukemia, in addition to increased or decreased white blood cells, decreased red blood cells may also be seen. 3. Platelet count. The normal value of platelets is 100 to 300×109/liter. If the platelets are below 80×109/liter in several tests, it is called thrombocytopenia, which can be seen in primary or secondary thrombocytopenia, aplastic anemia, acute leukemia or after X-ray irradiation. Platelet increase can be due to tissue damage injury and after surgery such as after splenectomy, thrombocytosis, etc.