What does a positive Antistreptolysin O (ASO) titer indicate?

A positive Antistreptolysin O (ASO) titer indicates a streptococcal infection. This test measures the presence of antibodies against streptolysin O, a substance produced by group A Streptococcus (the bacteria responsible for infections such as strep throat, scarlet fever, and rheumatic fever). When the body is exposed to these bacteria, it responds by producing antibodies, which can be detected through the ASO test.

Elevated ASO titers are often used as a diagnostic tool to confirm recent streptococcal infections or to assess the potential complications that can arise from them, such as rheumatic fever or post-streptococcal glomerulonephritis. The timing and interpretation of ASO results are important, as levels can rise within a week or two after an infection and may remain elevated for some time.

In contrast, a positive ASO titer would not indicate a viral or fungal infection, nor would it specifically point to a systemic infection, as these conditions involve different pathogens and typically elicit different immune responses. Hence, while elevated ASO levels specifically suggest exposure to group A Streptococcus, they provide limited information regarding other types of infections.