The reason why doctors give blood tests when a patient has gastroenteritis is to get a preliminary idea of the type of infection and the severity of the infection. If the routine blood results indicate elevated white blood cells and neutrophils, it means that it is a bacterial infection. The more elevated the white blood cells are, the more serious the infection is. If the routine blood results indicate that the white blood cells and neutrophils are normal or reduced, while the lymphocytes are significantly elevated, it means that the gastroenteritis should be caused by a viral infection, also known as a gastrointestinal cold, and the medication can be guided according to the routine blood results. If a patient with gastroenteritis wants to clarify the specific lesions of the gastrointestinal mucosa, an electronic gastroscopy and an electronic colonoscopy are required. The next step in the diagnosis and treatment can only be done after a specific hospital visit.