Routine blood test for viral infection

The main manifestations of viral infection include fever, headache, general discomfort and other systemic poisoning symptoms. It is particularly easy to cause viral infection when the human body's immunity is reduced. Viral infection will cause a series of symptoms to the body. Routine blood test is the most common and basic blood test, which tests the cellular part of the blood. What is the relationship between viral infection and blood routine tests? Today, let's follow the footsteps of science to understand the blood routine test for viral infection:

Taking blood to check the white blood cells and their cell classification is the most accurate and fastest way to determine the cause of infection. Acute high fever is mainly caused by infection, but it is difficult to determine the nature of the infection by blood tests within 24 hours of fever. Sometimes, if a child's blood is checked just a few hours after having a fever, it is not easy to detect an increase in white blood cells. An increase in white blood cells is the body's response to bacterial invasion. Well, since it is a "reaction" it naturally takes a certain amount of time to be noticed. This "perception" usually refers to the white blood cell count exceeding 10×109/L (the normal value of white blood cell count is 4 to 10×109/L). Since each person's normal baseline white blood cell count is different, the consensus "detectable" level can only be reached when the white blood cell count exceeds 10×109/L. The time it takes for each person's white blood cell to reach this level is different, so checking the white blood cell count at least 24 hours after infection (generally after a fever) is helpful in determining whether it is a viral or bacterial infection.

Of course, the number of white blood cells alone is not accurate enough. When checking the number of white blood cells, the white blood cells must be classified. White blood cells can be divided into neutrophils, lymphocytes, monocytes, eosinophils, alkaliphils, etc. Among them, the number of neutrophils increases more than 70% during bacterial infection, and the number of lymphocytes increases more than 50% during viral infection. If the number of neutrophils increases while the white blood cell count increases, it is more consistent with bacterial infection and antibiotic treatment should be used; if the number of lymphocytes increases while the white blood cell count is "normal" or slightly decreased, it is more consistent with viral infection.

Blood leukocyte and differential examinations can only preliminarily analyze bacterial or viral infections, but cannot determine what type of bacteria or virus it is. For more serious infections, local secretion culture, blood antigen or antibody testing and culture are required. Once a bacterial infection is suspected, doctors often use broad-spectrum antibiotics; for viral infections, especially respiratory infections, they often use drugs for symptoms such as runny nose and cough, or traditional Chinese medicine such as clearing heat and detoxifying.