Anti-streptolysin O

Anti-streptolysin O (ASO) is an antibody that is produced by the body's immune system in response to an infection with group A Streptococcus, the bacteria responsible for diseases such as strept throat, rheumatic fever, and scarlet fever. The ASO test is a measure of the body's immune response to the infection.

Overview

The ASO test is used to determine if a recent strep infection with group A Streptococcus is the cause of glomerulonephritis (a type of kidney disease) or rheumatic fever. The test measures the amount of ASO in the blood. A high level of ASO can be a sign of an ongoing or recent strep infection.

Procedure

The ASO test is a simple blood test. A healthcare provider will take a blood sample from a vein in your arm using a small needle. After the needle is inserted, a small amount of blood is collected into a test tube or vial. The blood sample is then sent to a laboratory for analysis.

Interpretation

A high ASO level can indicate a recent or ongoing infection with group A Streptococcus. However, a negative ASO test does not rule out a strep infection. Some people do not produce significant amounts of ASO, even when they have a strep infection. Therefore, the ASO test should be used in conjunction with other tests and clinical findings to diagnose strep infections.

Limitations

The ASO test is not specific for rheumatic fever or glomerulonephritis. It can be elevated in other conditions, including tonsillitis, pneumonia, and skin infections. Furthermore, the ASO level can remain elevated for several months after a strep infection, so it cannot be used to determine if an infection is current or recent.

See also

• Streptococcal infection
• Rheumatic fever
• Glomerulonephritis