This test is useful for measuring the amount of a particular type of antibody (called antistreptolysin) that is specifically produced upon contact with these bacteria. More precisely, antistreptolysin serves to counteract streptolysin, a haemolytic protein produced by some streptococci (group A, C and G).
If the antistreptolysin titer is low or the test is negative it means that a streptococcal infection has not occurred. A high or increasing value may, on the other hand, signal a recent exposure to the pathogen.
Streptococcus is mainly responsible for infections of the throat (pharyngitis, tonsillitis, etc.) and of the skin, which can cause serious complications, such as acute glomerulonephritis, rheumatic fever and endocarditis.
Once the presence of the bacterium has been ascertained with the dosage of the antistreptolysin title and other tests, it is possible to intervene with a targeted antibiotic therapy.
in response to "streptococcal infection. More precisely, it is synthesized to neutralize the haemolytic properties of streptolysin O, a protein produced by most of the streptococcal strains of group A and many of those belonging to groups C and G. The letter" O "indicates that this immunogenic toxin is labile to oxygen.
Streptolysin O is one of the two hemolysins (the other is streptolysin S) produced by practically all strains of Streptococcus pyogenes (or group A beta hemolytic streptococcus). In addition to causing hemolysis of red blood cells, this toxin has direct toxic effects on heart tissue.
The antistreptolysin title is also called with the abbreviation TAS (abbreviation of "Title Anti Streptolysin") and the acronyms ASLO or ASLOT (from the "English" AntiStreptoLysin O Titer ").
Streptococcus: basics
Streptococcus is a very common pathogen. This bacterium is typically localized in the upper respiratory tract, where it is able to cause pharyngotonsillitis: when the body is weakened, streptococcus multiplies near the oral cavity, causing high fever (up to 39-40 ° C), chills , bad breath, swelling of the tonsils, difficulty swallowing and whitish plaques in the throat Streptococcus is responsible for a variety of other infections, including those of the skin, such as pyoderma, impetigo and cellulitis.
In most cases, streptococcal infections are identified and managed with antibiotic therapy until the disease is resolved.
However, if an infection does not present clear symptoms, is not detected and eradicated with targeted therapy, the bacterium remains latent in the body, infiltrating vital organs, such as the heart or kidneys. This can lead to post-streptococcal complications, especially dangerous in young children, such as glomerulonephritis (inflammation of the kidney glomeruli), rheumatic fever or myocarditis. The secondary consequences of these pathologies are quite serious and include heart failure and renal dysfunction.
with the examination of the antistreptolysin titre, it is necessary to wait at least one week from the moment in which the streptococcal infection was contracted. In fact, antistreptolysin is not immediately produced, but increases 7 days after the infection, reaching a peak within 4-6 weeks, and then decreases when the infection is resolved and returns to normal values after a period of time that can last even a year.
Consequently, the antistreptolysin titer test cannot be used for the diagnosis of acute infections. In these cases, however, a rapid strep test or throat swab (culture) can be performed.
When is the exam prescribed?
In general, the dosage of the antistreptolysin titre is required a few weeks after the onset of symptoms indicative of pharyngotonsillitis and / or a streptococcal skin infection.
Therefore, the evaluation of the TAS is indicated by the physician when the patient exhibits some of the following symptoms:
- Sore throat;
- Fever;
- Chest pain;
- Fatigue;
- Palpitations;
- Breathing difficulty;
- Edema;
- Dark urine
- Rash;
- Swelling or pain in the joints.
To understand if the antistreptolysin titre has increased, decreased or remained stable, the doctor can schedule the execution of this examination even twice, within ten days of each other, in order to obtain the ASO titers. furthermore, to distinguish a state of convalescence from an "infection in progress.
The antistreptolysin titer test can also be prescribed if the doctor suspects that the patient has a disease resulting from a recent streptococcal infection, not previously identified and eradicated with targeted therapy. The examination is then requested upon the appearance of symptoms indicative of rheumatic fever or glomerulonephritis, to support the diagnosis.
Related exams
The antistreptolysin titer is positive only in about 80% of streptococcal infections, so a negative test does not necessarily rule out the diagnosis (note: the TAS can be low or negative if the infection is caused by strains that are poor producers of streptolysin O ). Likewise, undergoing exclusively the TAS examination has proved of little use, as the strep infection may have already passed.
For this reason, the antistreptolysin titer is frequently prescribed together with the ESR, ie the determination of the erythrocyte sedimentation rate (inflammatory index). If both of these parameters are positive, it means that the streptococcal infection is in progress. In this case, it is advisable to do other tests, to evaluate what type of treatment is necessary to put in place to solve the problem.
Determination of the antistreptolysin titer may be required alone or in conjunction with the test for anti-DNase B (anti-deoxyribonuclease B), another test used to assess the presence of a recent streptococcal infection. Especially measured when there is a suspicion of a false negative (20% of cases), this last parameter, when combined with the ASO titer, can detect up to 95% of streptococcal infections.
;A high value of the antistreptolysin titre compared to the reference one may also indicate the presence of more serious post-streptococcal diseases, complications of previous infections that are not well treated, such as:
- Endocarditis;
- Myocarditis;
- Glomerulonephritis;
- Rheumatic fever;
- Toxic shock syndrome.
Post-streptococcal complications: a brief note
The introduction of rapid tests for the diagnosis of these infections has decreased the frequency of these complications, which are however still present. The antistreptolysin titer can be used to determine whether these pathological conditions are indeed the consequence of a recent streptococcal infection.
, even in the case of the evaluation of the TAS, there may be factors that influence the outcome of the examination. For example, taking certain antibiotics and corticosteroids can decrease antibody levels.False negative antistreptolysin titer results may also result from liver disease and tuberculosis.
