What is the endpoint for the antistreptolysin O (ASO) latex agglutination assay?

The endpoint for the antistreptolysin O (ASO) latex agglutination assay is determined by identifying the highest serum dilution that shows agglutination. This is critical because the ASO test is designed to detect the presence of antibodies against streptolysin O, a toxin produced by Streptococcus bacteria.

In this assay, when serum containing ASO antibodies is diluted and mixed with latex particles coated with streptolysin O, visible agglutination occurs if antibodies are present in the serum. The highest dilution at which agglutination is still observed is interpreted as the endpoint, which reflects the titer of antibodies present. Thus, it tells us the maximum dilution that retains the ability to cause agglutination, indicating that antibodies are still present and functional at that dilution level.

Identifying this endpoint is essential for clinical diagnostics, as it helps quantify the serological response to streptococcal infections, assisting healthcare practitioners in diagnosing conditions such as rheumatic fever or glomerulonephritis associated with recent streptococcal infections.