SAA is serum amyloid A. This protein is an acute time-phase reactive protein that is mainly produced in the liver. In other words, when acute infection occurs in human body, the concentration of serum amyloid A will increase significantly, and various infections, including viral infection, bacterial infection, parasitic infection, mycoplasma infection, etc., will cause a significant and sensitive increase in SAA concentration, often within 4-8 hours of infection. For example, if a febrile patient has an abnormally high SAA but no significant increase in C-reactive protein, the diagnosis can be confirmed as an acute viral infection.