Streptolysin is an exotoxin produced by group A streptococci, referred to as anti-“O” or ASO. It can dissolve red blood cells and is toxic to many kinds of cells in the body. After the human body is infected with hemolytic streptococcus, a large amount of anti-streptococcal hemolysin O (anti-“O”) antibodies can appear in the serum. Detection of anti-“O” can be used as an auxiliary diagnosis of allergic diseases (rheumatic fever, glomerulonephritis) after streptococcal infection.