Blood tests are used to determine whether an infection is viral or bacterial, mainly from a combination of white blood cell and classification counts. Routine blood count is to use a blood analyzer to count the number of red blood cells, white blood cells and platelets in each liter of blood, to determine the volume of blood cells, certain biological characteristics and the content of certain substances in the blood cells, to determine whether there is any abnormality in the quality and quantity of the blood cells and other blood components, and it is the first choice of examination items for infection. In viral infections, the white blood cell count is mostly normal or lowered, accompanied by a lowered lymphocyte count and a lowered percentage of lymphocytes, which are common in diseases such as typhoid fever and paratyphoid fever. In bacterial infections, the white blood cell count is often elevated, and the neutrophil count and neutrophil percentage are also relatively elevated, such as purulent tonsillitis. If abnormal blood counts are found during the examination, it is recommended to complete the examination in time, clarify the cause of the disease, and then standardize the treatment under the guidance of the doctor to avoid delaying the condition.