Blood routine ultrasensitive C-reactive protein, which is an indicator of inflammation, used to be commonly used clinically to diagnose rheumatoid arthritis. Because it is more sensitive, it can be used as an indicator of infection, and an elevated level can indicate the presence of inflammation in the body. Nowadays, clinical flu and fever are also subjected to routine blood ultrasensitive examination, which can well indicate that there is bacterial or viral infection in the body, and it is the body’s acute inflammatory immune response protein. This value is of great benefit in guiding clinical treatment, so it is now routinely used not only in arthritis, but also in other febrile illnesses.