A high fever with ultra-sensitive C-reactive protein indicates that the body is in the acute phase of an infection. When the body is acutely infected, the level of ultra-sensitive C-reactive protein can increase by nearly 1,000-fold within a few hours, and can reach its peak in 1-3 days. With the control of inflammation, C-reactive protein levels will gradually decrease and return to normal, so monitoring blood C-reactive protein values can understand the growth and decline of inflammation, which is clinically important. In addition, the changes in the level of ultrasensitive C-reactive protein can be an important reference for disease monitoring and the results of drug therapy. Therefore, an increase in ultrasensitive C-reactive protein in fever indicates that the body is in the acute phase level of infection, and the higher the C-reactive protein level, the more severe the infection.