How to interpret the result of ASO titer?

Dear Sir,

The group A β-hemolytic streptococci produces various toxins that can act as antigens. One of these exotoxins Streptolysin O was discovered by Todd in1932.

A person infected with group A β-hemolytic streptococci produces specific antibodies against these exotoxins, one of which is antistreptolysin O (ASO). The quantity of this antibody in a patient's serum will establish the degree of infection due to the β-hemolytic streptococcal.2

The usual procedure for the determination of the anti-streptolysin titer is based on the inhibitory effect that the patient's serum produces on the hemolytic power of a pre-titrated and reduced Streptolysin O.

However, the antigen-antibody reaction occurs independently of the hemolytic activity of Streptolysin O. this property enables the establishment of a qualitative and quantitative test for the determination of the ASO by agglutination of latex particles on slide

This test is done if you have symptoms of a previous infection by group A Streptococcus. Some illnesses caused by these bacteria are:

·                     Bacterial endocarditis

·                     Glomerulonephritis, a kidney problem

·                     Rheumatic fever , which can affect the heart, joints, or bones

·                     Scarlet fever

·                     Strep throat

The ASO antibody may be found in the blood weeks or months after the strep infection has gone away. Normal value ranges may vary slightly among different laboratories.

A negative test result means you have likely not had a recent strep infection. The healthcare provider may repeat the test again in2 -4 weeks. Sometimes a test that was first negative will come back positive.

Abnormal results may be due to:

·                     Active streptococcal infection

·                     Bacterial endocarditis

·                     Post-streptococcal glomerulonephritis

·                     Rheumatic fever

·                     Scarlet fever

An abnormal or positive test means you recently had a strep infection, even if you had no symptoms. The ASO test may stay positive (sometimes called detectable) for2 to4 months afterward you are first infected.

-                     For this test, as in all serological tests, hemolytic or contaminated serum must not be used, and DO NOT USE PLASMA.

-                     Results should be read two (2) minutes after the mixing of the reagent on the slide. A reading obtained after this period of time may be incorrect.

-                     Existence of prozone at high titers has not been encountered.

-                     Although normal values can vary with age, season of the year and geographical area, the "upper limit of normal" ASO titers for preschool children is less than100 IU/ml and in school age children or young adults is usually between166 and250 IU/ml. In any case, the average can be established at less than200 IU/ml.

-                     Because of this variation, titers above the upper limits may be indicative of a streptococcal infection, but only a two dilution rise in titer between acute and convalescent stage specimens should be considered significant.

-                     Following acute streptococcal infection, the ASO titer will usually rise after one week, increasing to a maximum level within3 to5 weeks and usually returning to the pre-infection levels in approximately6 to12 months.

-

INTERPRETATION OF RESULTS:

n    Agglutination indicates an ASO content of more than200 IU/ml in the specimen.

n    Sera with positive results in the qualitative test should be retested in the semi-quantitative test.

The lack of agglutination indicates an ASO level lower than200 IU/ml in the sample. 

The ASO antibody may be found in the blood weeks or months after the strep infection has gone away.

A negative test result means you have likely not had a recent strep infection. The healthcare provider may repeat the test again in2 -4 weeks. Sometimes a test that was first negative will come back positive.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

An abnormal or positive test means you recently had a strep infection, even if you had no symptoms. The ASO test may stay positive (sometimes called detectable) for2 to4 months afterward you are first infected.