Part of
Infection & inflammation
Part of
Infection & inflammation
Blood biomarker
Part of
Infection & inflammation
Antistreptolysin O (ASO)
Antistreptolysin O (ASO)
Antistreptolysin O (ASO) measures antibodies produced against streptococcal bacteria.
Antistreptolysin O (ASO) measures antibodies produced against streptococcal bacteria.
Antistreptolysin O (ASO)
Normal range
Normal range
<200 IU/mL
<200 IU/mL
Normal range
<200 IU/mL
<200 IU/mL
Normal range
Antistreptolysin O (ASO)
Antistreptolysin O (ASO)
Antistreptolysin O (ASO) measures antibodies produced against streptococcal bacteria.
Antistreptolysin O (ASO)
Normal range
<200 IU/mL
Normal range
<200 IU/mL
<200 IU/mL
Normal range
Antistreptolysin O (ASO)
Antistreptolysin O (ASO)
Antistreptolysin O (ASO) measures antibodies produced against streptococcal bacteria.
Antistreptolysin O (ASO)
Normal range
<200 IU/mL
Normal range
<200 IU/mL
<200 IU/mL
Normal range
Antistreptolysin O (ASO)
Dr. Jack Devin
MBBS
Your Body's Memory of Streptococcal Battles
Your Body's Memory of Streptococcal Battles
ASO is your immune system's lasting record of encounters with Group A Streptococcus bacteria, the culprit behind strep throat, scarlet fever, and more serious invasive infections. When these bacteria invade your body, they release a toxin called streptolysin O, and your immune system responds by producing antibodies against it—these are your ASO antibodies. Unlike antibodies that provide ongoing protection, ASO serves primarily as a diagnostic marker, revealing recent or past streptococcal infections even when the original illness may have seemed minor or gone unnoticed. When ASO levels are elevated, they tell a story of immune battle, helping doctors understand whether symptoms like joint pain, kidney problems, or heart issues might be connected to a recent strep infection and potentially serious post-infectious complications.
ASO is your immune system's lasting record of encounters with Group A Streptococcus bacteria, the culprit behind strep throat, scarlet fever, and more serious invasive infections. When these bacteria invade your body, they release a toxin called streptolysin O, and your immune system responds by producing antibodies against it—these are your ASO antibodies. Unlike antibodies that provide ongoing protection, ASO serves primarily as a diagnostic marker, revealing recent or past streptococcal infections even when the original illness may have seemed minor or gone unnoticed. When ASO levels are elevated, they tell a story of immune battle, helping doctors understand whether symptoms like joint pain, kidney problems, or heart issues might be connected to a recent strep infection and potentially serious post-infectious complications.
When ASO Levels Are Elevated
When ASO Levels Are Elevated
When ASO Levels Are Elevated
Understand what raised ASO means about recent streptococcal infections and why this matters for your health.
Read more
Why ASO Testing Matters
Why ASO Testing Matters
Why ASO Testing Matters
Learn how this antibody marker helps diagnose serious post-streptococcal complications like rheumatic fever and kidney disease.
Read more
What Influences Your ASO Levels?
What Influences Your ASO Levels?
What Influences Your ASO Levels?
From the severity of strep infections to individual immune responses, discover what affects these important antibody levels.
Read more
Understanding Your Results
Understanding Your Results
Understanding Your Results
Decode your blood test numbers and know what your ASO levels reveal about past infections and potential complications.
Read more
When ASO Levels Are Elevated
Elevated ASO indicates your immune system encountered Group A Streptococcus and responded. ASO typically rises 1–3 weeks after infection, peaks around 3–5 weeks, and then gradually declines over 6–12 months. High ASO alone doesn’t confirm active infection but confirms recent exposure, and is a consideration when assessing possible post‑streptococcal complications.
Common symptoms of initial Group A strep infections include:
Sore throat with pain when swallowing
Red, swollen tonsils
Fever
Swollen lymph nodes in the neck
Headache or stomach pain
Sandpaper-like rash (scarlet fever)
Recognised, although individually rare, post-streptococcal complications include:
Rheumatic fever: May inflame heart valves, cause migrating joint pain, skin nodules, or neurological symptoms,
Post‑streptococcal glomerulonephritis: Occurs ~1–3 weeks after throat infection or ~3–6 weeks after skin infection, presenting with dark urine, facial swelling, and elevated blood pressure.
Tics (in children): Sudden onset of OCD or tics linked to strep exposure.
Elevated ASO levels alone don't diagnose these conditions but provide evidence that a recent strep infection occurred, helping doctors piece together the clinical picture when there are other or persistent symptoms present.
It's important to note that not everyone who has a strep infection will develop elevated ASO levels—about 20% of people don't produce significant ASO responses.
When ASO Levels Are Elevated
Elevated ASO indicates your immune system encountered Group A Streptococcus and responded. ASO typically rises 1–3 weeks after infection, peaks around 3–5 weeks, and then gradually declines over 6–12 months. High ASO alone doesn’t confirm active infection but confirms recent exposure, and is a consideration when assessing possible post‑streptococcal complications.
Common symptoms of initial Group A strep infections include:
Sore throat with pain when swallowing
Red, swollen tonsils
Fever
Swollen lymph nodes in the neck
Headache or stomach pain
Sandpaper-like rash (scarlet fever)
Recognised, although individually rare, post-streptococcal complications include:
Rheumatic fever: May inflame heart valves, cause migrating joint pain, skin nodules, or neurological symptoms,
Post‑streptococcal glomerulonephritis: Occurs ~1–3 weeks after throat infection or ~3–6 weeks after skin infection, presenting with dark urine, facial swelling, and elevated blood pressure.
Tics (in children): Sudden onset of OCD or tics linked to strep exposure.
Elevated ASO levels alone don't diagnose these conditions but provide evidence that a recent strep infection occurred, helping doctors piece together the clinical picture when there are other or persistent symptoms present.
It's important to note that not everyone who has a strep infection will develop elevated ASO levels—about 20% of people don't produce significant ASO responses.
When ASO Levels Are Elevated
Elevated ASO indicates your immune system encountered Group A Streptococcus and responded. ASO typically rises 1–3 weeks after infection, peaks around 3–5 weeks, and then gradually declines over 6–12 months. High ASO alone doesn’t confirm active infection but confirms recent exposure, and is a consideration when assessing possible post‑streptococcal complications.
Common symptoms of initial Group A strep infections include:
Sore throat with pain when swallowing
Red, swollen tonsils
Fever
Swollen lymph nodes in the neck
Headache or stomach pain
Sandpaper-like rash (scarlet fever)
Recognised, although individually rare, post-streptococcal complications include:
Rheumatic fever: May inflame heart valves, cause migrating joint pain, skin nodules, or neurological symptoms,
Post‑streptococcal glomerulonephritis: Occurs ~1–3 weeks after throat infection or ~3–6 weeks after skin infection, presenting with dark urine, facial swelling, and elevated blood pressure.
Tics (in children): Sudden onset of OCD or tics linked to strep exposure.
Elevated ASO levels alone don't diagnose these conditions but provide evidence that a recent strep infection occurred, helping doctors piece together the clinical picture when there are other or persistent symptoms present.
It's important to note that not everyone who has a strep infection will develop elevated ASO levels—about 20% of people don't produce significant ASO responses.
Why ASO Testing Matters
ASO testing serves as a vital diagnostic tool because it provides retrospective evidence of streptococcal infection when the original illness may have been missed, mild, or forgotten. This is particularly important because some of the most serious streptococcal complications develop weeks after the acute infection resolves.
Post-Streptococcal Complications
Rheumatic fever is perhaps the most common concern, as it can cause heart damage through inflammation of heart valves, particularly the mitral and aortic valves. Early symptoms include joint pain that moves between different joints, skin rashes, and heart rhythm abnormalities.
Post-streptococcal glomerulonephritis affects the kidneys' filtering units and typically develops 1-3 weeks after a strep throat or 3-6 weeks after a skin strep infection. Symptoms include dark or cola-coloured urine, facial swelling especially around the eyes, high blood pressure, and reduced urine output. Whilst most people recover completely, some may develop chronic kidney problems.
Why ASO Testing Matters
ASO testing serves as a vital diagnostic tool because it provides retrospective evidence of streptococcal infection when the original illness may have been missed, mild, or forgotten. This is particularly important because some of the most serious streptococcal complications develop weeks after the acute infection resolves.
Post-Streptococcal Complications
Rheumatic fever is perhaps the most common concern, as it can cause heart damage through inflammation of heart valves, particularly the mitral and aortic valves. Early symptoms include joint pain that moves between different joints, skin rashes, and heart rhythm abnormalities.
Post-streptococcal glomerulonephritis affects the kidneys' filtering units and typically develops 1-3 weeks after a strep throat or 3-6 weeks after a skin strep infection. Symptoms include dark or cola-coloured urine, facial swelling especially around the eyes, high blood pressure, and reduced urine output. Whilst most people recover completely, some may develop chronic kidney problems.
Why ASO Testing Matters
ASO testing serves as a vital diagnostic tool because it provides retrospective evidence of streptococcal infection when the original illness may have been missed, mild, or forgotten. This is particularly important because some of the most serious streptococcal complications develop weeks after the acute infection resolves.
Post-Streptococcal Complications
Rheumatic fever is perhaps the most common concern, as it can cause heart damage through inflammation of heart valves, particularly the mitral and aortic valves. Early symptoms include joint pain that moves between different joints, skin rashes, and heart rhythm abnormalities.
Post-streptococcal glomerulonephritis affects the kidneys' filtering units and typically develops 1-3 weeks after a strep throat or 3-6 weeks after a skin strep infection. Symptoms include dark or cola-coloured urine, facial swelling especially around the eyes, high blood pressure, and reduced urine output. Whilst most people recover completely, some may develop chronic kidney problems.
What Influences Your ASO Levels?
Factors That Can Raise ASO
Several factors influence how high your ASO levels become after streptococcal infection:
Severity and duration of the initial strep infection
Individual immune system responsiveness—some people naturally produce stronger antibody responses
Multiple or repeated strep infections, which can cause cumulative antibody rises
Factors That Can Affect ASO Interpretation
Several considerations can influence ASO test interpretation:
Recent antibiotic treatment may reduce ASO response if given very early in infection
Some people (approximately 20%) don't produce significant ASO responses even after proven strep infections
Liver disease can occasionally cause elevated ASO levels unrelated to strep infection
What Influences Your ASO Levels?
Factors That Can Raise ASO
Several factors influence how high your ASO levels become after streptococcal infection:
Severity and duration of the initial strep infection
Individual immune system responsiveness—some people naturally produce stronger antibody responses
Multiple or repeated strep infections, which can cause cumulative antibody rises
Factors That Can Affect ASO Interpretation
Several considerations can influence ASO test interpretation:
Recent antibiotic treatment may reduce ASO response if given very early in infection
Some people (approximately 20%) don't produce significant ASO responses even after proven strep infections
Liver disease can occasionally cause elevated ASO levels unrelated to strep infection
What Influences Your ASO Levels?
Factors That Can Raise ASO
Several factors influence how high your ASO levels become after streptococcal infection:
Severity and duration of the initial strep infection
Individual immune system responsiveness—some people naturally produce stronger antibody responses
Multiple or repeated strep infections, which can cause cumulative antibody rises
Factors That Can Affect ASO Interpretation
Several considerations can influence ASO test interpretation:
Recent antibiotic treatment may reduce ASO response if given very early in infection
Some people (approximately 20%) don't produce significant ASO responses even after proven strep infections
Liver disease can occasionally cause elevated ASO levels unrelated to strep infection
Understanding Your Results
ASO levels are measured in International Units per millilitre (IU/ml) or sometimes as titre dilutions:
Normal (Adults): <200 IU/ml
Elevated: Above these thresholds, with higher levels suggesting more recent or severe infection
However, reference ranges can vary between laboratories, and some labs report results as titres (e.g., 1:200, 1:400) rather than units.
Your ASO results should always be interpreted in conjunction with your clinical symptoms and history. A single elevated ASO level confirms recent streptococcal exposure but doesn't automatically indicate post-streptococcal complications. Your doctor will consider your symptoms, physical examination findings, and other test results to determine clinical significance.
ASO levels typically peak 3-5 weeks after initial infection and then gradually decline over several months.
Understanding Your Results
ASO levels are measured in International Units per millilitre (IU/ml) or sometimes as titre dilutions:
Normal (Adults): <200 IU/ml
Elevated: Above these thresholds, with higher levels suggesting more recent or severe infection
However, reference ranges can vary between laboratories, and some labs report results as titres (e.g., 1:200, 1:400) rather than units.
Your ASO results should always be interpreted in conjunction with your clinical symptoms and history. A single elevated ASO level confirms recent streptococcal exposure but doesn't automatically indicate post-streptococcal complications. Your doctor will consider your symptoms, physical examination findings, and other test results to determine clinical significance.
ASO levels typically peak 3-5 weeks after initial infection and then gradually decline over several months.
Understanding Your Results
ASO levels are measured in International Units per millilitre (IU/ml) or sometimes as titre dilutions:
Normal (Adults): <200 IU/ml
Elevated: Above these thresholds, with higher levels suggesting more recent or severe infection
However, reference ranges can vary between laboratories, and some labs report results as titres (e.g., 1:200, 1:400) rather than units.
Your ASO results should always be interpreted in conjunction with your clinical symptoms and history. A single elevated ASO level confirms recent streptococcal exposure but doesn't automatically indicate post-streptococcal complications. Your doctor will consider your symptoms, physical examination findings, and other test results to determine clinical significance.
ASO levels typically peak 3-5 weeks after initial infection and then gradually decline over several months.
The Takeaway
Anti-Streptolysin O antibodies serve as your immune system's historical record of battles with Group A Streptococcus bacteria, providing information weeks or months after the original infection. Whilst elevated ASO levels don't cause symptoms themselves, they help doctors identify when current health problems might be connected to previous streptococcal infections.
If your ASO levels are elevated, this doesn't mean you have complications, but it does provide information that helps your healthcare provider put any current symptoms in context.
The Takeaway
Anti-Streptolysin O antibodies serve as your immune system's historical record of battles with Group A Streptococcus bacteria, providing information weeks or months after the original infection. Whilst elevated ASO levels don't cause symptoms themselves, they help doctors identify when current health problems might be connected to previous streptococcal infections.
If your ASO levels are elevated, this doesn't mean you have complications, but it does provide information that helps your healthcare provider put any current symptoms in context.
The Takeaway
Anti-Streptolysin O antibodies serve as your immune system's historical record of battles with Group A Streptococcus bacteria, providing information weeks or months after the original infection. Whilst elevated ASO levels don't cause symptoms themselves, they help doctors identify when current health problems might be connected to previous streptococcal infections.
If your ASO levels are elevated, this doesn't mean you have complications, but it does provide information that helps your healthcare provider put any current symptoms in context.
References
Gerber, M. A., Baltimore, R. S., Eaton, C. B., et al. (2009). Prevention of rheumatic fever and diagnosis and treatment of acute Streptococcal pharyngitis. Circulation, 119(11), 1541-1551.
Carapetis, J. R., Steer, A. C., Mulholland, E. K., et al. (2005). The global burden of group A streptococcal diseases. The Lancet Infectious Diseases, 5(11), 685-694.
Rodriguez-Iturbe, B., & Musser, J. M. (2008). The current state of poststreptococcal glomerulonephritis. Journal of the American Society of Nephrology, 19(10), 1855-1864.
British Heart Foundation. (2020). Rheumatic heart disease: Prevention and management guidelines.
European Society of Cardiology. (2022). Guidelines for the management of patients with valvular heart disease.
References
Gerber, M. A., Baltimore, R. S., Eaton, C. B., et al. (2009). Prevention of rheumatic fever and diagnosis and treatment of acute Streptococcal pharyngitis. Circulation, 119(11), 1541-1551.
Carapetis, J. R., Steer, A. C., Mulholland, E. K., et al. (2005). The global burden of group A streptococcal diseases. The Lancet Infectious Diseases, 5(11), 685-694.
Rodriguez-Iturbe, B., & Musser, J. M. (2008). The current state of poststreptococcal glomerulonephritis. Journal of the American Society of Nephrology, 19(10), 1855-1864.
British Heart Foundation. (2020). Rheumatic heart disease: Prevention and management guidelines.
European Society of Cardiology. (2022). Guidelines for the management of patients with valvular heart disease.
References
Gerber, M. A., Baltimore, R. S., Eaton, C. B., et al. (2009). Prevention of rheumatic fever and diagnosis and treatment of acute Streptococcal pharyngitis. Circulation, 119(11), 1541-1551.
Carapetis, J. R., Steer, A. C., Mulholland, E. K., et al. (2005). The global burden of group A streptococcal diseases. The Lancet Infectious Diseases, 5(11), 685-694.
Rodriguez-Iturbe, B., & Musser, J. M. (2008). The current state of poststreptococcal glomerulonephritis. Journal of the American Society of Nephrology, 19(10), 1855-1864.
British Heart Foundation. (2020). Rheumatic heart disease: Prevention and management guidelines.
European Society of Cardiology. (2022). Guidelines for the management of patients with valvular heart disease.
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