Blood testing is a method of drawing peripheral blood from a patient and examining the number, shape, and ratio of various cells in the blood, as well as examining the various solute components of the blood. Blood tests are of great importance, such as a patient with a respiratory tract infection who presents with fever, cough and sputum. For example, in a patient with fever, cough and sputum, a routine blood test reveals an abnormally high white blood cell count, with a predominantly high neutrophil count, in which case the infection can be identified as being caused by bacteria and treated with sensitive antibacterial drugs. Similarly, a patient with a respiratory tract infection who presents with cough, fever and sputum, but whose routine blood tests reveal a mild decrease in the white blood cell count and an increase in the lymphocyte ratio, can be determined to be caused by a viral infection based on the routine blood tests, and will need to be treated with antiviral medication.