Ultrasensitive C-reactive protein is a protein that reacts with S. pneumoniae C polysaccharide. Ultrasensitive C-reactive protein activates complement, promotes phagocytosis, and has immunomodulatory effects. If in clinical practice, an ultrasensitive C-reactive protein greater than 5 is often seen in purulent inflammatory conditions, such as purulent tonsillitis, or a boil on a part of the body, or in necrotic tissue, such as in burns or trauma, or in rheumatic diseases, ultrasensitive C-reactive protein will appear high. According to clinical experience, a C-reactive protein greater than 5 can be observed and rechecked in two weeks for targeted treatment.