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 toxin “foreign Ag” produced by Lancefield group A streptococci “ streptococcus pyogens”.
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

3. Significance of ASOT
ASOT 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.

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 antibody may be detected in the blood for weeks or months after the primary source of infection has eradicated.
Incidence of detect a positive result during the :-
3rd weak of infection %
2 month %
6 month %
12 month %
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.
Incidence decreases as the time increseases
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 collected in plain tubes.
Principle of the test :
A stabilized buffered suspension of polystyrene latex particles have been coated with streptolysin O Ag 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 phenomena.
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.

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 - - + + - +
Back to 200
1600
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 “

9. Note :
The test reaction must be read immediately within 2-3 minutes, as Delayed readings may result in false positive result.