The group A ï¢-hemolytic streptococci produces various toxins that can act as antigens. One of these exotoxins Streptolysin O was discovered by Todd in 1932. 1
A person infected with group A ï¢-hemolytic streptococci produces specific antibodies against these exotoxins, one of which is antistreptolysin O (ASO). The quantity of this antibody in a patient's serum will establish the degree of infection due to the ï¢-hemolytic streptococcal. 2
The usual procedure for the determination of the antistreptolysin titer is based on the inhibitory effect that the patient's serum produces on the hemolytic power of a pretitrated and reduced Streptolysin O. 2-6 However, the antigen-antibody reaction occurs independently of the hemolytic activity of Streptolysin O. 7 this property enables the establishment of a qualitative and quantitative test for the determination of the ASO by agglutination of latex particles on slide. 2

PRINCIPLE
ASO test method is based on an immunological reaction between streptococcal exoenzymes bound to biologically inert latex particles and streptococcal antibodies in the test sample. The reagent has been adjusted in the way that presence of an ASO titer of 200 IU/mL or higher in the serum gives a visible agglutination of the latex particles without previous sample dilution.