Anti-streptococcal hemolysin “O” is an antibody produced by the body after infection with group A hemolytic streptococci. If the level of anti-streptococcal hemolysin “O” is found to be elevated, it indicates the presence of group A hemolytic streptococcal infection in the human body. group A hemolytic streptococci are a group of common human infections with strong antigenicity. When the human body is infected with group A hemolytic streptococci, streptococcal hemolysin “O” will stimulate the B lymphocytes in the human immune system to produce the corresponding antibodies, namely anti-streptococcal hemolysin “O”, the level of which can be found to be increased by blood tests. Generally speaking, after 2 weeks of infection with group A hemolytic streptococci, the level of anti-streptococcal hemolysin “O” can be detected in the blood and can reach the highest level after about 4 weeks, after which it slowly decreases and takes more than 6 weeks to drop to normal level. Many clinical diseases are associated with infection with group A hemolytic streptococci, so the detection of anti-streptococcal hemolysin “O” level can help the diagnosis and treatment of such diseases, such as rheumatic fever, rheumatic heart disease, scarlet fever, infective endocarditis, streptococcal-associated nephritis. Therefore, once an elevated anti-streptococcal hemolysin “O” level is detected, you should immediately go to the hospital to improve the examination and further search for the cause.