The ASO test is primarily used to help determine whether a recent strep infection with group A Streptococcus:

• It is the cause of a person’s or glomerulonephritis, a form of kidney disease
• Caused rheumatic fever in a person with signs and symptoms
  
  

The test may be ordered by itself or along with an anti-DNase B, another test used to detect recent strep infections. In most cases, strep infections are identified and treated with antibiotics and the infections resolve. In cases where they do not cause identifiable symptoms and/or go untreated, however, complications, namely rheumatic fever and glomerulonephritis, can develop in some people, especially young children. The test, therefore, is ordered if a person presents with symptoms suggesting rheumatic fever or glomerulonephritis and has had a recent history of sore throat or a confirmed streptococcal infection.