Anti-streptolysin O


Anti-streptolysin O is the antibody made against streptolysin O, an immunogenic, oxygen-labile streptococcal hemolytic exotoxin produced by most strains of group A and many strains of groups C and G Streptococcus bacteria. The "O" in the name stands for oxygen-labile; the other related toxin being oxygen-stable streptolysin-S. The main function of streptolysin O is to cause hemolysis — in particular, beta-hemolysis.
Increased levels of ASO titre in the blood could cause damage to the heart and joints.
In most cases, penicillin is used to treat patients with increased levels of aso titre.

Clinical significance

When the body is infected with streptococci, it produces antibodies against the various antigens that the streptococci produce. ASO is one such antibody. A raised or rising levels can indicate past or present infection. Historically it was one of the first bacterial markers used for diagnosis and follow up of rheumatic fever or scarlet fever. Its importance in this regard has not diminished.citation neededcitation needed|date=July 2020

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.

Mechanism of action

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

Antistreptolysin O titre

Antistreptolysin O titre O titer or AS is a measure of the blood plasma levels of antistreptolysin O antibodies used in tests for the diagnosis of a streptococcal infection or indicate a past exposure to streptococci.The ASOT helps direct antimicrobial treatment and is used to assist in the diagnosis of scarlet fever, rheumatic fever, and post infectious glomerulonephritis.
A positive test usually is >200 units/mL, but normal ranges vary from laboratory to laboratory and by age.
The false negatives rate is 20-30%. If a false negative is suspected, then an anti-DNase B titre should be sought. False positives can result from liver disease and tuberculosis.