Anti Streptolysin O (ASO / ASLO)

Clinical definition of the Anti Streptolysin O (ASO) test
Antistreptolysin O (ASO) are antibodies produced by the body in response to infection with Group A Streptococcus bacteria. These antibodies produced against the bacteria cross react with human antigens (mainly collagen) and hence attack various organs, mainly the heart, joints, skin, brain, etc.

Why is the Anti Streptolysin O (ASO) test done?
ASO tests are generally used to diagnose and monitor the treatment of a streptococcal infection or indicate a past exposure to the bacteria which may cause rheumatism, scarlet fever and glomerulo nephritis.

What are the common signs/symptoms when the Anti Streptolysin O (ASO) test is done?

  • Fever
  • Chest pain
  • Fatigue
  • Shortness of breath
  • Edema
  • Other symptoms associated with rheumatic fever or glomerulonephritis
  • Abdominal pain
  • Joint pain
  • Arthritis (mainly in the knees, elbows, ankles, and wrists)
  • Joint swelling
  • Redness or warmth
  • Nosebleeds
  • Skin nodules
  • Skin rash 

Who should do the Anti Streptolysin O (ASO) test (Target population)?
Persons showing the above signs & symptoms or those who may have had a history of infection with streptococci bacteria.

What should I do before the Anti Streptolysin O (ASO) test?

Specimen type

Specimen collection procedure

Preparatory instructions before the test *

Serum (Blood Sample)

Venipuncture - Collection of blood from a vein, usually from the arm.

No Fasting Required.

No other special preparations required.

*Subjects suffering from any illness or on oral or injectable medications are advised to consult their physician prior to requesting any tests or procedures.

How do I interpret my Anti Streptolysin O (ASO) test results?

Reference Range*


Below 200 IU/ml


Inference: If a false negative is suspected, then an anti-DNase B titre should be sought. False positives can result from liver disease and tuberculosis.
‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’

Diseases/conditions related to the Anti Streptolysin O (ASO) test

  • Active streptococcal infection
  • Bacterial endocarditis
  • Post-streptococcal glomerulonephritis
  • Rheumatic fever
  • Scarlet fever
  • Glomerulonephritis
  • Rheumatic fever
  • Scarlet fever

Other tests related to the Anti Streptolysin O (ASO) test

  • Haemogram
  • Electrocardiogram (ECG)
  • Sedimentation rate (ESR)
  • Anti- dsDNA

Synonyms : ASO titer
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ASO Titre