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ASO Titre Test

ASO Titre Test is also called the Streptolysis O Titre Test. ASO means Anti Streptolysin O. Antistreptolysin O (ASO) are antibodies produced by our immune system and present in our blood against a Toxin called Streptolysin O. Antibodies against ASO reach a maximum at 3 to 6 weeks after infection. ASO titers are usually elevated in Streptococcal upper respiratory tract infections while skin infection will not elicit a strong ASO response.

What is Streptolysin O?

Streptolysin O is a toxin Produced by group A Streptococcus. The main bacteria in group A Streptococcus is (Streptococcus Pyogenese). The infection is caused by Streptococcal Infection.

  • Throat Infection
  • Cellulitis
  • Pyoderma
  • Impetigo

Purpose of ASO Test?

This test is performed when the doctor suspects that the patient has symptoms of rheumatic fever or Glomerulonephritis and may be due to group A streptococcus (Streptococcus Pyogenese)

Symptoms in ASO Positive Patients?

  1. Pain in joints and swelling
  2. Fever and blood in urine
  3. Skin Rash and high blood pressure
  4. Nodule under skin
  5. Body pain, Chest pain, Shortness of breath

Normal Range of ASO Titre Test?

  1. ASO Titre(By Agglutination Method) = Less than 200 IU/mL
  2. ASO Titre(By Nephelometery Method)
  • Less than 5 Years Age: Less than 10 IU/mL
  • 5 to 17 Years Age: 10-15 IU/mL
  • More than 18 Years Age: More than 15 IU/mL

ASO Test Methods

The anti-streptolysin O (ASO) test was devised by Todd. ASO is expressed in Todd units.

  • Neutralization of RBC lysis by Streptolysin O
  • Latex agglutination test
  • Nephelometric method
  • Turbidimetric method

Specimen Collection for ASO Titre Test

  • Collect 5 to 7 ml of blood in a gel Top tube.
  • Centrifuge the blood sample and separate the serum.
  • The patient’s serum can be done by using Agglutination or Nephelometric Method and the test can be done qualitatively and quantitatively.
  • Qualitatively estimation of ASO the slide is labeled for positive control negative control and test sample
  • Then add one drop of positive control to the well and a drop of negative control then add a drop of serum
  • In this case, add 50 microliter of the test serum and one drop of ACE origin to each of the circles
  • Once the reagent is added we have to mix the reagents using separate applicator sticks for each surface
  • After mixing rock the slide to and fro for two minutes look for the clumping of latex particles in the test sample if you visible blue donations then it indicates the test sample contains titres of more than two hundred torrents.


  • ASO Titre = Highest dilution of serum showing agglutination X sensitivity of the test
  • This Particular demonstration: Sensitivity of the test = 200 Todds unit
  • Highest dilution serum showing agglutination=16
  • ASO Titre =16 x 200
  • ASO Titre = 3200 Todd units/ml
  • Myeloma
  • Hypergammaglobulinemia
  • Liver disease
  • Autoimmune disease with elevated rheumatoid factor


  • Endemic area: A single positive test significant
  • Non-endemic area: A paired test should done. The two-fold rise in ASO is diagnostic.
  • Children:> 400 Todd units
  • Adults:> 200 Todds units
  • The ASO test remains the best standardized most reproducible, and most universal.
  • A 2-foil rise in antibody titers is regarded as definitive proof of an antecedent Streptococcus pyogenes infection.


  1. What is the ASO Titre blood test?
    • The ASO Titre blood test is a diagnostic test used to measure the levels of anti-streptolysin O antibodies in the blood.
  2. What are anti-streptolysin O antibodies?
    • Anti-streptolysin O antibodies are produced by the immune system in response to an infection by Group A Streptococcus bacteria. The ASO test helps identify the presence of these antibodies in the blood.
  3. Why is the ASO Titre test performed?
    • The test is often used to diagnose a recent streptococcal infection, such as strep throat, or other complications like rheumatic fever or glomerulonephritis.
  4. How is the test performed?
    • The ASO Titre test is a blood test. A healthcare professional will draw a small amount of blood from a vein, usually from the arm.
  5. What do the results indicate?
    • Elevated levels of anti-streptolysin O antibodies suggest a recent or current infection with Group A Streptococcus bacteria.
  6. What conditions are associated with high ASO Titre levels?
    • Elevated ASO Titre levels are often associated with streptococcal infections, but they can also be indicative of complications like rheumatic fever or glomerulonephritis.
  7. Are there any factors that can affect ASO Titre test results?
    • Certain medications and medical conditions can potentially influence the results, so it’s essential to inform the healthcare provider about any ongoing treatments or health issues.
  8. How is a high ASO Titre treated?
    • Treatment depends on the underlying cause. Antibiotics are commonly prescribed to treat streptococcal infections, and other conditions may require specific therapies.

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