Home Biomarkers ASO (quantitative)

ASO (quantitative)

Arthritis Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Arthritis

Overview

Antistreptolysin O (ASO) quantitative measures antibodies directed against streptolysin O, a toxin produced by Group A Streptococcus (GAS). The test estimates whether a recent streptococcal infection has occurred—useful when considering complications such as acute rheumatic fever, post‑streptococcal reactive arthritis, or post‑streptococcal glomerulonephritis. Symptoms prompting testing include recent sore throat, fever, migratory joint pains, new heart murmurs, rash, or blood in the urine. ASO titers typically rise 1–3 weeks after infection, peak around 3–5 weeks, and decline over months; children and populations with higher GAS exposure often have higher baseline titers. Sex differences are minimal; reference ranges vary by lab and region.

People also test for

Test Preparation

No special preparation is required

Why Do I Need This Test

Profile: included in Arthritis/inflammatory complication workups.
Symptoms: recent pharyngitis, fever, migratory arthritis, carditis, hematuria.
Conditions: helps diagnose/monitor rheumatic fever, post-streptococcal reactive arthritis, PSGN.
Abnormal levels: indicate recent or past GAS exposure; very high values suggest recent infection.
Causes: untreated/treated strep throat, close-contact outbreaks, repeated exposures.
Family history of rheumatic fever or recurrent streptococcal disease raises suspicion.

Run our symptom checker to see if this test is right for you

Symptom Checker

Understanding Test Results

Values <200 IU/mL are generally considered normal/negative for recent significant GAS exposure.
Results of 200–400 IU/mL are equivocal or may reflect recent past exposure; correlate with symptoms and consider repeat testing.
Levels >400 IU/mL suggest a recent streptococcal infection and support diagnoses such as acute rheumatic fever or post‑streptococcal arthritis when clinical features are present; values >800 IU/mL are strongly suggestive of recent/robust immune response.
Note timing: ASO can be falsely low in the first week after infection—paired acute and convalescent samples showing a rising titer (twofold or greater) are most diagnostic.
Immunosuppressed patients may have blunted responses; skin infections may elevate anti‑DNase B more than ASO.

Normal Range

0-200 IU/mL

FAQs

Q: What is a quantitative test for ASO?

A: A quantitative test for antistreptolysin O (ASO) measures ASO antibody concentration in blood, reported in IU/mL. It's usually performed by nephelometry or enzyme immunoassay to give a numeric titer; rising or elevated levels indicate recent Group A streptococcal infection and can support diagnoses like rheumatic fever or glomerulonephritis. Results must be interpreted with clinical context and lab reference ranges.

Q: What does it mean if ASO is high?

A: A high ASO (antistreptolysin O) titer means the immune system has recently been exposed to Streptococcus bacteria. It suggests a recent or recent-past strep infection and can be seen with complications such as rheumatic fever or post-streptococcal glomerulonephritis. ASO rises 1–3 weeks after infection, peaks around 3–5 weeks, and may remain elevated for months; clinical correlation and further testing are needed.

Q: What is ASO quant?

A: ASO (anti‑streptolysin O) is a blood test that measures antibodies to streptolysin O, a toxin from group A Streptococcus. It helps detect recent or prior strep infection when complications (e.g., rheumatic fever, post‑streptococcal glomerulonephritis) are suspected. Results are reported as a titre; a high or rising titre in paired samples suggests recent infection. It supports, but doesn’t alone confirm, diagnosis.

Q: What is a normal ASO level?

A: A normal antistreptolysin O (ASO) titre is generally considered below about 200 IU/mL in adults; in children the usual upper limit is lower, often around 120 IU/mL. Reference ranges vary between laboratories and populations. Mild to moderate rises can reflect past streptococcal exposure, while markedly elevated titres suggest recent or ongoing infection; clinical correlation and repeat testing are often needed.

Q: Is ASO positive curable?

A: ASO positivity isn't a disease to \

Q: What are the symptoms of streptococcus?

A: Symptoms of Streptococcus (group A) include sudden sore throat, pain when swallowing, fever, red/swollen tonsils often with white patches or pus, and tender swollen neck lymph nodes. Children may have headache, stomach pain, nausea/vomiting, or a fine red rash (scarlet fever). Skin infections cause local redness, swelling, warmth, pain, blisters or honey‑coloured crusts (impetigo).