The Agappe ASO 50Test, or Anti-Streptolysin O (ASO) test, is a diagnostic tool used to detect and quantify the levels of ASO antibodies in human serum. These antibodies are produced by the body in response to an infection with Group A Streptococcus bacteria. Elevated ASO levels can indicate recent or current streptococcal infections and may be associated with complications like rheumatic fever and glomerulonephritis.