The blood test is the most common test for children, because it includes many items, many parents are worried when they get the results and see that there are many abnormalities inside. In fact, we only need to look at a few major aspects, 1, white blood cells (wbc) such as fever children we mainly look at the number of white blood cells and their classification, in general, if the number of neutrophils increased is a bacterial infection, lymphocytes increased is a viral infection, normal pediatric white blood cells at birth up to (15 ~ 20) × 109 / L, and then gradually decline, the average of 15 × 109 / L at 1 week. The most common cause of increased leukocytes is acute bacterial infections, especially septic bacterial infections. In contrast, hypocytosis is most often seen in viral infections, certain bacterial infections such as typhoid fever, malaria, and cornual tuberculosis. In addition to the white blood cell count, the ratio of various white blood cell types is also an important criterion for determining infection. The most important thing to look at clinically is the change in the ratio of neutrophils to lymphocytes. In the case of neutrophils, for example, the significance of increased and decreased neutrophils is generally roughly the same as the total white blood cell count, i.e., increased neutrophils indicate a bacterial infection and decreased indicates a viral infection. It is worth noting that some newborns with poor resistance to infection often do not have an increase in total leukocyte count, while neutrophils are still significantly elevated, indicating a more serious infection. 2. Hemoglobin (HGB) Hemoglobin is related to anemia, and our Pediatric Hematology Society stipulates that hemoglobin is less than 145 g/L in the neonatal period, less than 90 g/L from 1 to 4 months, and less than 100 g/L from 4 to 6 months as anemia. The causes of anemia are insufficient hemoglobin production, hemolytic anemia and blood loss anemia. In children, nutritional anemia, such as iron deficiency anemia, is the most common cause, which is characterized by a decrease in mean red blood cell volume (MCV), mean red blood cell hemoglobin volume (MCH), and mean red blood cell hemoglobin concentration (MCHC), and is a small cell hypochromic anemia. If the MCV is less than 60, it is usually recommended to take a blood test for thalassemia gene. The normal value of platelets is (100-300) 109/L. Platelets are mainly related to blood clotting function and can be caused by serious infectious diseases such as septicemia. Idiopathic thrombocytopenic purpura. Leukemia. Infectious diseases such as dengue fever. Platelets are increased by diseases such as primary thrombocytosis and sometimes by viral infections in children, which can cause a transient increase in platelets.