The clinical significance of ultrasensitive C-reactive protein 40mg/L lies mainly in the following four points: First, it is the most sensitive and specific indicator of acute inflammatory response syndrome, such as during acute immune response to peripheral infections, and ultrasensitive C-reactive protein 40mg/L occurs during acute inflammatory infections of the periphery, such as acute respiratory tract infection, acute pneumonia, acute gastroenteritis, acute peritonitis, and acute appendicitis. Second, ultrasensitive C-reactive protein will also increase and appear positive during severe trauma and large body blows, such as stress reactions to trauma, blood loss, surgery, etc. Third, within 6 months of acute myocardial infarction, ultrasensitive C-reactive protein 40 mg/L is also seen in the blood system and is clinically significant. Fourth, it is occasionally seen in rheumatic diseases, connective tissue diseases and immune system diseases.