Streptolysin-O is an enzyme produced by the beta-hemolytic streptococci of group A. When confronted with this foreign enzyme, the body produces antibodies against it. Antibodies appear 7 to 10 days after acute streptococcal infection and continue to increase for 2 to 4 weeks. Anti-streptolysin-O (ASTO) levels usually fall to the pre-infection level at 6 to 12 months. ASTO (or ASO) screening is designed to detect these antibodies. If the antibodies are positive, the patient has or has had a streptococcal infection.
Over 80% of patients with acute rheumatic fever and 95% of patients with acute streptococcal glomerulonephritis have elevated ASTO levels. ASTO levels usually do not increase in skin infections. Determination of anti-streptolysin-O is considered less sensitive than anti-DNase B testing. When both tests are performed simultaneously on blood samples, they can determine 95% of streptococcal infections.
ASTO measurement is particularly useful in the diagnosis of rheumatic fever and post-streptococcal glomerulonephritis, two diseases resulting from group A beta-hemolytic streptococcal infections. The ASTO measurement does not predict whether complications will occur after streptococcal infection, nor does it predict the severity of the disease.
Possible Interpretations of Pathological Values
- Increase: Rheumatic fever, post-streptococcal endocarditis, post-streptococcal glomerulonephritis, scarlet fever.
- Decrease: Medications: antibiotics, corticosteroids.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.