Antistreptolysic (ASO)

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Latest Edit: Hector 2014-03-21 (EDT)

See Also Lab Tests

This test is used mainly to determine whether a previous streptococcus infection has caused a poststreptococcal disease, such as glomerulonephritis, rheumatic fever, bacterial endocarditis, and scarlet fever.[1]


  • ASO, or antistreptolysic O titer is a seroligic procedure that shows the body's reaction to infection caused by group A beta-hemolytic streptococci.
  • Streptococcus organisms produce an enzyme called streptolysin O, which can destroy red blood cells.
  • Therefore, the body reacts to the antigenic streptolysin O by producing ASO, a neutralizing antibody.
  • ASO can appear in the serum 1 week to a month after the onset of a streptococcal infection, levels appearing higher in glomerulonephritis and rheumatic fever.

Patient Preparation

  • No fasting required.
  • Factors which can cause increased levels
  • Increased beta-lipoprotein levels can neutralize streptolysic O and appear as increased ASO levels
  • Factors which can cause decreased levels
  • Drugs: antibiotics and adrenocorticosteroids

Clinical Implications

High levels indicate:

  • Acute streptococcal infection
  • Acute rheumatic fever
  • Bacterial endocarditis
  • Acute glomerulonephritis
  • Scarlet fever
  • Streptococcal pyoderma

Associated Tests

  • Antideoxyribonuclease-B Titer


  1. Pagana Kathleen D, Pagana Timothy J (2006) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby.