Lab Test

Antistreptolysin O (ASO)

ASO, ASLO, Streptolysin O Antibodies, Streptococcal Antibodies, ASO Titer (Anti-Streptolysin O Antibody), Anti-Strep dNase B

Test Codes

Antrim #30961, EPIC: LAB5238, ASO



Specimen Collection Criteria

Collect: One Gold-top SST tube.

Physician Office/Draw Specimen Preparation

Let specimen clot 30–60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2–8°C or 36–46°F) the centrifuged collection tube within eight hours of collection.

Preparation for Courier Transport

Transport: Centrifuged collection tube, refrigerated (2–8 °C or 36–46 °F). (Minimum: 0.5 mL Serum)

Rejection Criteria

  • Grossly lipemic specimens.
  • Hemolyzed specimens.
  • Plasma specimens.
  • Specimens that have gross bacterial contamination.
  • Specimens not collected and processed as indicated.

In-Lab Processing

Let specimen clot 30–60 minutes then immediately centrifuge to separate serum from cells. Deliver immediately to the appropriate testing station.


Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers® with Separator Gels
Room Temperature (20–26°C or 68–78.8°F): 8 hours
Refrigerated (2–8°C or 36–46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers® without Separator Gels
Room Temperature (20–26°C or 68–78.8°F): 2 hours
Refrigerated (2–8°C or 36–46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20–26°C or 68–78.8°F): 8 hours
Refrigerated (2–8°C or 36–46°F): 7 days
Frozen (-20°C/-4°F or below): 3 months

Specimen Storage in Department Prior to Disposal:

Refrigerated (2–8°C or 36–46°F): 7 days


Dearborn Chemistry Laboratory
Royal Oak Automated Chemistry Laboratory


Sunday – Saturday.
Results available within 24 hours of receipt in the Laboratory.

Reference Range

0–4 Years of Age: Less than 100 IU/mL.            
5–17 Years of Age: Less than 250 IU/mL.            
Adults: Less than 200 IU/mL.                             

Test Methodology



  • A negative ASO result can not rule out a previous streptococcal infection. Early use of penicillin prevents the ASO titer from rising. ASO titers are elevated in 85–90% of patients with acute rheumatic fever. ASO levels are elevated in only 30-40% of patients with impetigo and in 50% of patients with glomerulonephritis.
  • A two-fold or greater rise in ASO between acute and convalescent sera is suggestive of a recent Group A streptococcal infection.

Clinical Utility

Streptolysin O is one of several immunogenic exoenzymes produced by Group A, Beta-hemolytic streptococci. An elevated anti-streptolysin O (ASO) titer is usually indicative of a recent infection with a group A streptococci and is a routine part of the diagnosis and management of acute rheumatic fever and acute glomerulonephritis. In the absence of complications or reinfection, antibody levels usually fall to preinfection levels 6-12 months following infection.

Clinical Disease

  • Streptococcus pyogenes has long been implicated as an important cause of upper respiratory tract and cutaneous disease. The principal manifestations of S. pyogenes are strep throat, scarlet fever, and skin infections (impetigo and cellulitis). Necrotizing fasciitis (the so called flesh-eating bacterial infection) has also been caused by S. pyogenes. Rapid diagnosis and treatment of S. pyogenes infections is important to prevent complications associated with these infections. The most common complications include acute rheumatic fever and acute glomerulonephritis. Rheumatic fever may occur after strep throat in about 2-3% of cases. Glomerulonephritis may follow either pharyngeal or skin infection.
  • The most common symptoms of streptococcal pharyngitis include an abrupt onset of sore throat, malaise, headache, and a fever greater than 101°F. The throat is red with a grayish-white exudate on the tonsils.
  • Scarlet fever is caused by an exotoxin produced by a certain group of Beta-hemolytic Group A streptococci. The symptoms include a skin rash on the upper chest beginning on the second day of illness. The rash fades within a week and the skin may peel.
  • Impetigo is a superficial cutaneous infection characterized by crusted lesions. It typically occurs in late summer or early fall. It is most common in tropical or semitropical climates.
  • Necrotizing fasciitis is a life-threatening and sometimes fatal infection that affects previously healthy patients between 20-50 years old. Symptoms include fever, severe pain, redness, and swelling at the wound site.
  • Pyrogenic exotoxins similar to the toxic shock syndrome toxin 1 of S. aureus have been identified in these patients. People with chronic illness are at higher risk of acquiring invasive disease. Cuts, wounds, and chickenpox provide opportunity for bacteria to enter. Thirty percent of these patients die despite aggressive, seemingly appropriate therapy.
  • Rheumatic fever is characterized by inflammatory lesions that may involve the heart, joints, subcutaneous tissues, and central nervous system. It primarily occurs in children 6-15 years old with a recent history of Group A streptococcal pharyngitis. It may be prevented by treating the patient with antibiotics within 9 days of the onset of strep throat. Onset occurs approximately 20 days after infection.
  • Acute glomerulonephritis may be a complication of either pharyngitis or cutaneous infection. It is predominantly found in preschool and school-age children. It occurs 6-10 days after the onset of pharyngitis or 14-21 days after cutaneous infection. It is an acute inflammatory disease of the renal glomeruli. Virtually all patients have microscopic hematuria and proteinuria.


Streptococcal pharyngitis occurs year-round in temperate climates, but the incidence peaks in the winter and spring months. Infections can occur in any age group but most cases occur among school-age children.


Streptococcal infections are spread from person to person via inhalation of S. pyogenes laden respiratory droplets. Foodborne and milkborne transmission has also been described. A number of individuals, particularly school-age children, carry S. pyogenes without signs of illness. Carriers are culture positive and seronegative.

CPT Codes

86060, 5370-2


Last Updated


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