The ASO test is primarily used to help determine whether a recent strep infection with group A Streptococcus, 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 ASO test is done as a routine work-up to help determine whether a recent strep infection with group A Streptococcus: 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 (sequelae), 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.