( Antistreptolysin O Titer ) ASOT ( Antistreptolysin O Titer )

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

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.

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 90-95 % 2 month 70-75 % 6 month 35 % 12 month 20 % 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.

“ 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 “

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.

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

Comments on Results A raised or rising levels can indicate past or present infection. Elevated levels may indicate : 1. Active streptococcal infection. 2. Sore throat. 3. Rheumatic fever. 4. Scarlet fever. 5. Post-streptococcal glomerulonephritis. 6. Bacterial endocarditis. False positive results(rise in titer)may occur in : 1. High fibrinogen 2. Gross hemolysis 3. High lipid in serum 4. Oxizied reagent 5. Bacterial contamination “ dirty slide “

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