Anti Streptolysin O (ASO) Titre, Serum

ASO test is used for detection of antibodies to streptolysin O in human serum. ASO test is highly sensitive and specific test. Determination of these antibodies is very useful for the diagnosis of streptococcal infections and their relative effects such as rheumatic fever and acute glomerulonephritis, recent history of sore throat or diagnosed streptococcal infection. Streptococcal infection when identified, can be treated with antibiotics. However if not diagnosed or untreated, complications such as rheumatic fever, glomerulonephritis may develop. Rheumatic fever presents with symptoms like fever, chest pain, fatigue, shortness of breath and glomerulonephritis presents with symptoms such as edema, dark urine, etc. Especially in recent post Group A streptococcal infection. The group of Streptococci which produce soluble hemolysin are called ¯-hemolytic streptococci. These ¯-hemolytic streptococci are further divided into Group A, Group B, Group C, Group D. Group A Streptococci produces exotoxin Streptolysin O and Strepolysin S which act as antigens. During Streptococccal infection, specific antibodies against Streptolysin O and Streptolysin S are produced. The detection of these antibodies is useful in the diagnosis of Streptococcal infections. The antistreptolysin antibodies increase and peaks in the body between 3 to 8 weeks after the streptococcal infection. And the levels will remain high for several months. Steroids and certain antibiotics reduce the ASO antibody levels and hence make the interpretation of diagnosis difficult. An increased levels of ASO antibody titres indicate streptococcal infection. However if the ASO antibody titres is negative and still suspecting streptotoccal infection, it is advised to have a repeat test done for the confirmation or to rule out the infection. If the serum sample contain high protein, the ASO results may be non-specific. Another test used along with ASO is anti-DNase B which is used to detect recent Streptococcal infections.

1. Can ASO levels help to diagnose streptococcal infection?

ASO antibody levels in the body increase and become detectable for atleast one week after the streptococcal infection and hence this test is not useful for the diagnosis of acute infection. Throat culture is considered as the best method during acute phase of infection.

2. Is ASO test always needed, even after streptococcal infection is diagnosed?

ASO test is not done routinely. It is advised mostly if suspecting streptococcal infection, untreated infection, when there are symptoms suggesting complications of post streptococcal infection.

3. What is the Significance of the ASO test Result?

An increased levels of ASO antibody titres indicate streptococcal infection. However if the ASO antibody titres is negative and still suspecting streptotoccal infection, it is advised to have a repeat test done for the confirmation or to rule out the infection.