Anti-streptolysin O

Nomenclature

• Streptolysins are enzymes produced by beta hemolytic streptococci (Lancefeld Group A). These are either Streptolysin-S(stable) or Streptolysin-O(Oxygen labile.)
• Antibodies produced against this enzyme shows up in the blood of an infected individual are used in the diagnosis of these infections. These antibodies are called Anti-streptolysin-O or ASO, in abbreviation.

Significance

Historically and even presently, this bacterial marker was one of the earliest markers of rheumatism or scarlet fever.

Values

Since these antibodies are produced as a delayed hypersensitive reaction to the above mentioned bacteria, there is nothing called a "normal value." Any presence of these antibodies indicates an exposure to these bacteria. As many people get exposed to these bacteria, but remain asymptomatic, the mere presence on ASO does not indicate a serious disease.

Acceptable values, where there is no clinical feature of rheumatism are as follows:

• Adults: less than 200 units
• Children: less than 300 units

This titre (value) has a significance, only if it is greatly raised, or if a rise in titre can be demonstrated in paired blood samples taken days apart.

Values need to be correlated with a clinical diagnosis.

Estimation

It is done by serological methods like latex agglutination or slide agglutination. ELISA may be performed to detect the exact titre value.

To detect the titre value, by a non-ELISA method, one has to perform the above agglutination using a serial dilution technique.

• vide: serology for details.

Mechanism of action

These antibodies produced against the bacteria cross react with human antigens (mainly collagen) and hence attack the cellular matrix of various organs, mainly the heart, joints, skin, brain, etc.

• vide:rheumatic fever for details