Anti-Streptolysin O (ASO), Qualitative, Serum

What it is:
The ASO test (qualitative) detects the presence of antibodies against streptolysin O, a toxin produced by Group A Streptococcus bacteria. A positive test suggests a recent or past streptococcal infection, which may lead to post-streptococcal complications.

Uses

• Detect recent streptococcal infection (pharyngitis, scarlet fever, skin infection)

• Aid in diagnosing post-streptococcal complications, such as:

  • Rheumatic fever

  • Post-streptococcal glomerulonephritis

• Differentiate bacterial from non-bacterial causes of certain inflammatory conditions

Symptoms That May Lead to the Test

• History of sore throat or skin infection followed by:

  • Fever, joint pain, or swelling

  • Chest pain, shortness of breath (possible carditis)

  • Blood in urine, swelling (possible glomerulonephritis)

• Unexplained fever, fatigue, or inflammatory signs

Abnormal Results

• Positive ASO (qualitative):

  • Suggests recent Group A streptococcal infection

  • Alone, it does not confirm disease but supports diagnosis with clinical history and other tests

• Negative ASO:

  • No evidence of recent streptococcal infection

  • Does not exclude infection entirely, as some patients may not develop antibodies

Risks

• Minimal, limited to routine blood draw risks (mild pain, bruising, dizziness).