Antistreptolysin - O, Serum Quantitative

The Antistreptolysin O (ASO) test is a blood test that detects antibodies your body produces in response to an infection with group A Streptococcus bacteria. It helps determine whether a recent strep infection might have triggered complications in the body.

What is Antistreptolysin O (ASO)?

• Streptolysin O is a toxin produced by group A Streptococcus bacteria.
• The body responds by making antibodies called ASO antibodies.
• Measuring ASO levels in the blood shows if the body has recently fought a strep infection, even if symptoms are gone.

Why the Test Is Ordered

1. Suspected post-streptococcal complications

• Rheumatic fever (can affect heart, joints, brain, skin)
• Post-streptococcal glomerulonephritis (kidney inflammation)

2. History of recent strep infection

• Sore throat (pharyngitis)
• Skin infections (impetigo)
• Often used when complications appear weeks after the infection

3. Recurrent infections or unexplained symptoms

• Fever of unknown origin
• Joint pain or swelling
• Heart murmurs

More about the test

The ASO test is primarily used to detect a recent strep infection and help evaluate whether post-streptococcal complications like rheumatic fever or kidney inflammation may be developing.