IMMUNOLOGY
PAGE EXPIRES: June 2000
SYNONYMS: ASO, ASLO, ASO Titer, Streptolysin antibody
COMPONENT TESTS: None (single test)
SCHEDULE: Reference Lab turnaround time: 7 working days
SPECIMEN AND COLLECTION REQUIREMENTS:
CAUSES FOR REJECTION: Improperly labeled specimen; hemolysis, lipemia, or turbidity
STORAGE AND SHIPPING: Freeze serum for storage and shipping
USES: To confirm recent or on-going infection with beta-hemolytic streptococci; support diagnosing rheumatic fever and poststreptococcal glomerulonephritis in the presence of clinical symptoms; to distinguish between rheumatic fever and rheumatoid arthritis when joint pains are present.
NORMAL VALUES:
METHOD: Dual Beam Photonephelometry
DESCRIPTION AND COMMENTS: Streptolysin O is a hemolytic factor produced by most strains of Group A beta-hemolytic streptococci. Anti-Streptolysin O (ASO) is the specific neutralizing antibody produced after infection with these organisms. ASO appears in the serum from 1 week to 1 month after the onset of a streptococcal infection. The basis of the test is the neutralization of the hemolytic activity of the streptolysin O toxin for erythrocytes by specific antibodies in serum. Since this antigen is produced by nearly all strains of group A streptococci, a significant increase in titer of ASO strongly supports a diagnosis of recent group A streptococcal infection.
The ASO titer is elevated in approximately 80% of those streptococcal pharyngitis patients who develop acute rheumatic fever or glomerulonephritis. It is also elevated in 60% of patients with uncomplicated streptococcal disease. However, with streptococcal pyoderma, only 25% of patients show an elevation, even in the presence of glomerulonephritis. Antibiotic treatment during the streptococcal infection may abort or depress the antibody response. A four-fold rise in titer is considered significant.
The endpoint in each test is the highest dilution of serum that has no visible hemolysis; this endpoint is the titer that is reported. The titer can be expressed in International Units (IU) or Todd units, since the two measurements are essentially the same. The number of units is the same as the titer of that patient's serum.