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Antibodies to streptococci A, B, C, D, F, G in blood
Last reviewed: 05.07.2025
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Infections caused by streptococci A, B, C, D, F, G. Antibodies to streptococci A, B, C, D, F, G in blood serum
The titer of antibodies to streptococcus in the blood serum is normally 12-166 U.
Streptococci are among the most common pathogens of bacterial infections in humans. Based on antigenic differences, most streptococci isolated from humans are classified into groups A, B, C, D, F, G.
Group A streptococci are of exceptional importance because they often cause infectious diseases in humans and play a significant role in the development of rheumatism and glomerulonephritis.
Group B streptococci often inhabit the female genital tract and the mucous membranes of the pharynx and rectum.
Streptococci of groups C and G are considered commensals, but in some cases they can cause pharyngitis.
Group D streptococci are a common cause of urinary tract infections in patients with structural abnormalities and are the etiologic factor for bacterial endocarditis in more than 10% of cases.
The main method of diagnosing streptococcal infection is bacteriological. Recently, rapid slide tests have been developed (the answer can be obtained within 10 minutes) based on the immunochromatography method (sensitivity - 97%, specificity - 95%), allowing the detection of the antigen of β-hemolytic streptococcus group A in nasopharyngeal washes and β-hemolytic streptococci group B - in vaginal discharge. Serological diagnostics is based on the detection of the titer of antibodies to the polysaccharide of streptococcus group A by the ELISA method, as well as ASLO in the patient's blood serum.
Antibodies to group A streptococcal polysaccharide (anti-A-CHO) appear in the first week of infection, their titer rapidly increases, reaching a peak by the 3rd-4th week of the disease. A diagnostic value is an increase in antibody titer by at least 4 times after 10-14 days when studying paired sera. It should be borne in mind that even an active streptococcal infection causes a 4-fold increase in antibody titer only in 70-80% of patients. The test for antibodies to group A streptococcal polysaccharide is usually used as an addition to the detection of ASLO and antibodies to deoxyribonuclease B in patients with rheumatic fever. There is a highly specific correlation between the constant content of anti-A-CHO in the blood serum and the activity of rheumatic carditis. With effective treatment, the content of anti-A-CHO decreases several months later than other markers of streptococcal infection.
To diagnose streptococcal infection caused by other groups of streptococci, the ELISA method is used, which allows the detection of specific antibodies to carbohydrates of the bacterial wall, mainly groups C and G. However, these studies have not received widespread use.
Antibody titer to streptococci in various diseases
Diseases |
AT titer, U |
Active rheumatic fever |
500-5000 |
Inactive rheumatic fever |
12-250 |
Rheumatoid arthritis |
12-250 |
Acute glomerulonephritis |
500-5000 |
Streptococcal upper respiratory tract infection |
100-333 |
Collagenoses |
12-250 |
Determination of antibodies to streptococci is used to diagnose streptococcal infection in the following diseases:
- catarrhal, lacunar, follicular tonsillitis;
- erysipelas, scarlet fever, glomerulonephritis, rheumatism;
- septic conditions;
- chronic inflammatory lung diseases.
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