What is the principle of the antistreptolysin O (ASO) tube test?

The principle of the antistreptolysin O (ASO) tube test is based on hemolysis-inhibition. In this test, the presence of antistreptolysin O antibodies in a patient's serum is detected by mixing the serum with a streptolysin O preparation, which would normally cause hemolysis of red blood cells. If anti-ASO antibodies are present, they will bind to the streptolysin O and inhibit its hemolytic activity. This results in a lack of hemolysis, indicating a positive test result.

The hemolysis-inhibition principle is particularly useful in the diagnosis of streptococcal infections, such as post-streptococcal glomerulonephritis or rheumatic fever, where the body produces these antibodies in response to infection. Thus, detecting their presence through this method helps in clinical evaluations related to streptococcal infections.