C-reactive protein is abbreviated as CRP, and ultrasensitive C-reactive protein is customarily called hsCRP, which is essentially the same substance in terms of detection sensitivity. The C-reactive protein measured by immunoturbidimetric method of automatic biochemical instrument is usually customarily referred to as conventional C-reactive protein. This method has a high linear range, but the sensitivity is not good and does not accurately reflect changes in C-reactive protein below 10 mg/L. Ultrasensitive C-reactive protein assay can meet both high sensitivity and wide linearity. For example, latex immunoturbidimetric method and immunofluorescence dry quantification method, the above two methods are actually different in price. In clinical practice, conventional C-reactive protein is often applied as an acute temporal phase protein, which is rapidly elevated several hours after the onset of various acute inflammation, tissue injury, myocardial infarction, surgical injury, radiation injury and other diseases, and rapidly decreases to normal when the disease improves. For the above diseases, routine C-reactive protein measurement is usually sufficient. However, for newborns, the basic level of C-reactive protein is usually very low, and its change cannot be measured by conventional methods. Ultrasensitive C-reactive protein >2 mg/L indicates neonatal infection, and continuous elevation is more meaningful than single elevation. Ultrasensitive C-reactive protein is clinically more valuable for detecting pneumonia in patients with low leukocytes or immunocompromised, especially in pediatric and elderly patients. Ultrasensitive C-reactive protein is more sensitive than leukocytes in the early stages of HFMD infection, and serial testing is considered positive with ultrasensitive C-reactive protein >5 mg/L.