What is an ASO test and how is it used to detect a strep infection?
Antistreptolysin O (ASO) is a blood test used to help diagnose a current or past infection with group A strep (Streptococcus pyogenes). It detects antibodies to streptolysin O, one of the many strep antigens. This test is rarely ordered now compared to thirty years ago. For an acute strep throat infection, the ASO test is not helpful; the rapid strep test or throat culture should be used. However, if a doctor is trying to find out if someone had a recent strep infection that may not have been diagnosed, this test could be helpful. In addition, it may be used to help diagnose rheumatic fever or glomerulonephritis, which occurs weeks after a strep throat infection when the rapid strep and throat culture would no longer be positive.
