ASO titer

Antistreptolysin O (ASO) Titer

The Antistreptolysin O (ASO) titer is a blood test used to measure the level of antibodies against streptolysin O, a substance produced by Group A Streptococcus bacteria. This test is significant in diagnosing previous infections caused by these bacteria, most notably rheumatic fever and glomerulonephritis, which are post-streptococcal complications. The ASO titer is an important tool in the diagnosis and management of these conditions.

Overview

Streptococcus bacteria are responsible for a variety of health conditions, ranging from mild throat infections to more severe diseases such as rheumatic fever. Following an infection with Group A Streptococcus, the body produces antibodies against streptolysin O, a toxin released by these bacteria. The ASO titer test quantifies these antibodies to determine if a recent streptococcal infection has occurred.

Indications

The ASO titer test is indicated for patients who present with symptoms suggestive of post-streptococcal complications, such as:

• Rheumatic fever
• Post-streptococcal glomerulonephritis
• Unexplained heart valve abnormalities
• Recurrent sore throats or tonsillitis

Procedure

The ASO titer test is performed on a sample of the patient's blood. The procedure involves drawing blood from a vein, usually from the arm. The sample is then analyzed in a laboratory to measure the level of antistreptolysin O antibodies.

Interpretation of Results

A high ASO titer indicates a recent streptococcal infection. However, the interpretation of ASO titer results can be complex, as levels can vary based on age, geographical location, and the presence of other medical conditions. Elevated ASO titers are more significant if there is a rising trend in serial measurements.

Limitations

While the ASO titer test is useful in diagnosing recent streptococcal infections, it has its limitations. Not all patients who have had a streptococcal infection will develop elevated ASO titers. Additionally, elevated ASO levels can persist for months after an infection, potentially leading to confusion in diagnosis.

Conclusion

The ASO titer test is a valuable diagnostic tool in identifying recent infections with Group A Streptococcus, particularly in the context of suspected rheumatic fever or glomerulonephritis. Despite its limitations, when used in conjunction with clinical findings and other diagnostic tests, the ASO titer can provide crucial information for the diagnosis and management of post-streptococcal complications.