Group A streptococci produce several extracellular products including streptolysin O, hyaluronidase, streptokinase, desoxyribonucleases (DNAase A, B, C, D), and nicotinamide adenine dinucleotidase (NADase). Streptococcal infections can lead to serious complications of glomerulonephritis and rheumatic fever following a latency period of 10 to 20 days after the acute infection. Serologic detection of antibodies to these streptococcal antigens may provide evidence of previous streptococcal infection.
ASO titers are elevated in about 85% of individuals with rheumatic fever. Streptococcal skin infections, in contrast to throat infections, are associated with a poor ASO response. Therefore, patients who develop acute glomerulonephritis following a skin infection may not have a significant rise in anti-streptolysin O. In these instances, additional testing for anti-DNAse is recommended.
Prospective studies have provided important insight into the immune response to Streptococcal infection over an extended period of time. One hundred and sixty randomly selected children between the ages of 6 and 15 years (mean 10 years) had monthly throat cultures and serum collections every 13 weeks for measurement of anti-streptolysin O (ASO) and anti-DNase B (ADB) titers during an average observation period of 97 weeks. Each participant had an average of 21.8 throat cultures and 10.5 antibody titers during the study.
Approximately one third of the patients with Group A streptococcal infection had a positive throat culture and significant elevations of both ASO and ADB titers. In the remaining two thirds of cases, either ASO or ADB was elevated, but not both. Serological confirmation of infection would have been missed in 22% of cases if only one these antibodies had been ordered.
Group A, group C and group G streptococci all produce antigenically identical ASO and all three stimulate the same magnitude of ASO response. In contrast ADB is more specific for GAS infection. No ADB responses were seen following infection with group C or group G Streptococcus. Another interesting finding was that antibiotic treatment did not significantly affect ASO and ADB antibody responses even though bacteria were eradicated.
ASO can be detected by a nephelometer. The reference range for ASO is age dependent.
Specimen requirement is one SST tube of blood.
Reference
Johnson DR et al. The Human Immune Response to Streptococcal Extracellular Antigens: Clinical, Diagnostic, and Potential Pathogenetic Implications, Clinical Infectious Diseases 2010;50(4):481-90.
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