What does a positive ASO (antistreptolysin O) test mean?

Generally, a positive ASO (antistreptolysin O) test indicates that the level of ASO antibodies in the blood is above the normal reference range. The detailed analysis is as follows:

ASO, or antistreptolysin O, is an antibody produced in response to streptococcal cell wall components. After a streptococcal infection, the human body generates ASO antibodies to fight the infection. Elevated levels of ASO antibodies typically indicate a prior streptococcal infection and may suggest an ongoing streptococcal infection. ASO antibody levels gradually rise after infection, reaching a peak 1–3 weeks post-infection, then slowly decline. Therefore, elevated ASO levels may indicate a recent streptococcal infection. The ASO antibody test is a method used to detect streptococcal infection and is commonly employed in diagnosing conditions associated with streptococcus, such as rheumatic fever and acute glomerulonephritis. A positive ASO result indicates either a current or past streptococcal infection but cannot determine the exact timing or severity of the infection.

In summary, a positive ASO (antistreptolysin O) test means that the level of ASO antibodies in the blood exceeds the normal reference range, suggesting either a current or previous streptococcal infection. Clinical interpretation should be made in conjunction with other symptoms and diagnostic findings.