In general, the blood test after 24 hours of fever is more accurate for the reaction of the disease. If the blood test is done after 12 hours of fever, it can also reflect part of the disease, but often the degree of the disease is not as accurate as after 24 hours. However, if a child or adult has a severe fever, it is necessary to have an urgent blood test to confirm the type of infection so that targeted medication can be administered. Therefore, it is necessary to check the blood count at 12 hours of fever. If there is an elevation of white blood cells or neutrophils, it indicates a bacterial infection and anti-inflammatory treatment with antibiotics is needed immediately for better results. If the eosinophils are elevated, it may be a viral infection, and you need to use antiviral drugs to treat it with better results, such as Pu Di Lan Anti-inflammatory Oral Liquid, Four Seasons Antiviral Compound or Ribavirin Granules.