Ultrasensitive C-reactive protein is an acute phase reactive protein. Ultrasensitive C-reactive protein is an acute phase protein synthesized by hepatocytes when the body is subjected to inflammatory stimuli such as microbial invasion or organism injury.Ultrasensitive C-reactive protein is elevated within hours of the onset of inflammation and peaks in 48 hours, and its sensitivity and accuracy exceed that of C-reactive protein. Ultrasensitive C-reactive protein is not affected by treatments such as radiotherapy, chemotherapy, corticosteroids and immunoglobulins. Therefore, ultrasensitive C-reactive protein has a wide range of clinical applications, including the diagnosis and differential diagnosis of acute infectious diseases, the diagnosis of inflammatory bowel disease and autoimmune diseases, the detection of inflammatory indexes in the process of tumor radiotherapy, and the diagnosis of rejection reaction in transplantation. In summary, ultrasensitive C-reactive protein is a very widely used and effective test.