1. ( Antistreptolysin O Titer )
ASOT
( Antistreptolysin O Titer )

2. Alternative Names :-
ASO
ASLO
Anti-streptolysin O ( ASO or ASLO ) is an antibody produced against an antigen produced by Lancefield group A streptococci “ streptococcus pyogens”.
The the toxin is called streptolysin O, the O stands for oxygen-labile; the other toxin that secreted is an oxygen-stable “ streptolysin S ”.
Both toxins are involved in producing hemolysis, in particular, Beta-hemolysis.
S. Pyogens by gram stain
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.
Beta-hemolysis

3. Significance of ASOT
ASO testing is a procedure that demonstrate the presence of antibodies generated by the body against infections by group A streptococcus (S. pyogen) mostly for Tonsillitis and Rheumatic fever, this m/o produce the toxin streptolysin O, which cause destruction of RBCs cell walls.
This toxin is immunogenic, that is, the body produces antibodies against it.
Some symptoms of rheumatic fever may include:
Fever
Joint swelling and pain in more than one joint, especially in the ankles, knees, elbows and wrists, sometimes moving from one joint to another
Small, painless nodules under the skin
Rapid, jerky movements (Sydenham's chorea)
Skin rash
Sometimes the heart can become inflamed (carditis); this may not produce any symptoms but also may lead to shortness of breath, heart palpitations, or chest pain

4. Incidence of detect a positive result during the :-
Note that :-
Antibodies ( IgG ) begin to appear in patient serum 7-10 days after infection.
The ASO antibodies may be found in the blood weeks or months after the strep. infection has gone away.
Incidence of detect a positive result during the :-
3rd weak of infection %
2 month %
6 month %
12 month %
Incidence decreases as the time increseases
The antibody levels begin to rise after 1 to 3 weeks of strep infection, peaks in 3 to 5 weeks and falls back to insignificant levels in 6 months. Values need to be correlated with a clinical diagnosis.
The amount of ASO antibody (titer) peaks at about 3 to 5 weeks after the illness and then tapers off but may remain detectable for several months after the strep infection has resolved
If the titer doesn’t decrease with time ; this means that a recurrent or chronic infection may exist.

5. “ the reaction will occur within minutes “
ASOT test
What is it ?
It is a latex agglutination test for the qualitative screening and semi-quantitative determination of anti-streptolysin O antibodies in serum.
Specimen should be Serum in plain tubes.
Principle of the test :
A stabilized buffered suspension of polystyrene latex particles have been coated with streptolysin O when is mixed with a serum containing antibodies to streptolysin O ,agglutination occur.
“ the reaction will occur within minutes “

6. Results Interpretation
At Direct agglutination step :
No agglutination
serial dilution is done to exclude probability of prozone
The result is written less than 200 IU/ml,
Don’t write negative result
Agglutination is observed
This mean that ASO Level of 200 IU/ml or more, and so Serial dilution is done to detect the exact titer.
Titer is detected by multiplying dilution factor by 200 IU/ml
ليش قلنا 200 مش نيجاتيف لانه لازم احدنا يكون اصيب بهذه البكتيريا في مرحلة من المراحل

7. Semi-quantitative method
add 50ul
50ul
50ul
serum
50ul 1
50ul 2
50ul 3
And so on; NS NS NS
1:2
1:4
1:8
Total Dilution
agglutination - - + + - +
1600
Back to 200
800
Back to 400
Back to 800
Titer ( IU/ml ) =
400

8. Comments on Results
A raised or rising levels can indicate past or present infection.
Elevated levels may indicate :
1. Active streptococcal infection Sore throat
3. Rheumatic fever Scarlet fever
5. Post-streptococcal glomerulonephritis Bacterial endocarditis
False positive results(rise in titer)may occur in :
1. High fibrinogen Gross hemolysis
3. High lipid in serum Oxizied reagent
5. Bacterial contamination “ dirty slide “
An elevated titer of antibody (positive ASO) or an ASO titer that is rising means that it is likely that the person tested has had a recent strep infection.
ASO titers that are initially high and then decline suggest that an infection has occurred and may be resolving.

9. Note :
The test reaction must be read immediately within 2 minutes, as Delayed readings may result in false positive result.