Serum amyloid a, abbreviated as SAA, is an acute temporal protein produced by hepatocytes that is secreted into the serum. When the body is infected or injured, it can rise rapidly about 1000-fold within 4-6 hours, and then fall rapidly to normal levels when the body-antigen is cleared. SAA is a sensitive indicator for the diagnosis of viral bacterial infections, and in bacterial infectious diseases, it has the advantage of rising early, large amplitude and high sensitivity compared with C-reactive protein. Especially in the early detection of acute bacterial infection, the advantage of SAA is more significant.SAA in viral infectious disease, SAA will be significantly higher, but C-reactive protein does not rise, so SAA can be used as a sensitive indicator for the diagnosis of viral infection.SAA and C-reactive protein test, can be differential diagnosis of bacterial and viral infection, and can provide a new basis, more reliable, dynamic observation of the efficacy of treatment, and The SAA and C-reactive protein test can provide a new basis for differential diagnosis of bacterial and viral infections, a more reliable basis for dynamic observation of efficacy, and guidance for clinical use.