Antistreptolysin O (ASO) test

The Antistreptolysin O (ASO) test measures the level of antibodies produced by the immune system in response to a bacterial toxin called streptolysin O, produced by Streptococcus bacteria. Elevated ASO levels can indicate a recent or past streptococcal infection, such as strep throat or skin infections. This test is often used to help diagnose complications like rheumatic fever or glomerulonephritis that can follow a strep infection. It’s a blood test that provides clues about whether your immune system recently fought off a streptococcal bacteria.