ASO is the medical abbreviation of anti-streptococcal hemolysin O antibody, which is an antibody to hemolysin O, a metabolite with hemolytic activity produced by Streptococcus haemolyticus, and often appears within one week after streptococcal infection, and can gradually increase and then gradually decrease thereafter. Therefore, ASO can be significantly increased in a series of infectious diseases caused by streptococcal infections, such as acute pharyngitis, acute tonsillitis, dengue, scarlet fever, skin and soft tissue infections, infective endocarditis, etc. In addition, immunoreactive diseases associated with hemolytic streptococcal infections can also show elevated ASO, such as active rheumatic fever, glomerulonephritis after acute streptococcal infection, allergic purpura, rheumatoid arthritis, and rheumatic heart disease. Usually elevated ASO reflects past, not present, immune response and cannot be used as an acute reactant to evaluate the severity of rheumatic diseases, as well as other inflammatory states, nor can it be used as an indication for antibiotic use alone.