Anti-Streptolysin O (ASO)
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ASO antibodies are produced by the immune system in response to an infection caused by Group A Streptococcus (Streptococcus pyogenes). The bacteria secrete a toxin called streptolysin O, which is harmful to red blood cells. The ASO test detects antibodies against this toxin
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🧪 Anti-Streptolysin O (ASO) Test
Parameter | Details |
|---|---|
Full Name | Anti-Streptolysin O (ASO) Antibody Test |
Sample Type | Blood (Serum) |
Fasting Required | ❌ No |
Method | Nephelometry / Turbidimetry / Latex Agglutination |
Turnaround Time | 1–2 days |
🔬 What Is ASO?
ASO antibodies are produced by the immune system in response to an infection caused by Group A Streptococcus (Streptococcus pyogenes). The bacteria secrete a toxin called streptolysin O, which is harmful to red blood cells. The ASO test detects antibodies against this toxin.
🧠 Organs/System Involved
System | Role of ASO |
|---|---|
Immune system | Produces ASO antibodies in response to strep infection |
Heart, joints, kidneys | Targeted in post-streptococcal autoimmune complications |
🎯 Why Is This Test Done?
Purpose | Clinical Relevance |
|---|---|
✅ Detect recent streptococcal infection | Particularly if patient presents with delayed complications |
❤️ Diagnose rheumatic fever | After throat infection, especially in children |
🧠 Assess post-streptococcal glomerulonephritis (PSGN) | Kidney damage due to immune response |
🤒 Evaluate scarlet fever or strep-associated arthritis | Joint pain or fever following strep infection |
📊 Interpretation of Results
Result | Interpretation |
|---|---|
< 200 IU/mL (adults) | Normal, no recent streptococcal infection |
> 200 IU/mL (adults) | Possible recent or ongoing streptococcal infection |
> 300–400 IU/mL (children) | More likely post-streptococcal complication |
Levels start rising 1–3 weeks after infection, peak at 3–6 weeks, and return to normal in a few months.
🧬 Conditions Associated with Elevated ASO
Condition | Relation to ASO |
|---|---|
Rheumatic fever | Classic post-strep complication; often elevated ASO |
Post-streptococcal glomerulonephritis (PSGN) | Kidney damage after strep; ASO typically high |
Scarlet fever | Strep-related rash; ASO may rise |
Streptococcal pharyngitis | ASO may rise if untreated or partially treated |
Reactive arthritis | May follow strep infection |
🔁 Recommended Further Diagnostics
Test | Why It's Useful |
|---|---|
Anti-DNase B test | Another strep antibody, often ordered with ASO |
Throat culture or rapid strep test | Detect active Group A Streptococcus infection |
Urinalysis | Evaluate kidney involvement (e.g., hematuria, proteinuria) |
CBC (Complete Blood Count) | Check for infection-related changes (leukocytosis) |
ESR / CRP | Assess inflammation (especially in rheumatic fever) |
Echocardiogram / ECG | If suspecting carditis due to rheumatic fever |
👨⚕️ Who Should Get This Test?
- Children or adults with:
- Joint pain, fever, or rash weeks after sore throat
- Unexplained kidney symptoms (swelling, dark urine)
- Suspicion of rheumatic heart disease
- Delayed strep infection complications
📌 Summary Table
Test | Anti-Streptolysin O (ASO) |
|---|---|
Sample | Blood (Serum) |
Organ/System | Immune system, indirectly affects heart, joints, kidneys |
Associated Conditions | Rheumatic fever, PSGN, scarlet fever |
When Ordered | 2–4 weeks after strep symptoms or for unexplained immune symptoms |
Common Add-ons | Anti-DNase B, ESR, CRP, CBC, urinalysis |
Fasting Required | ❌ No |
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