Streptococcal Serology (Blood)

Diagnostic Use

Immunological testing for specific antibodies to streptococcal metabolites provides important information regarding a prior streptococcal infection (rheumatic fever, scarlet fever, tonsillitis, Glomerular nephritis, etc.) In various regions rheumatic fever has become a rarer occurrence, but mild or sub-clinical cases have increased, thus necessitating detailed clarification by serodiagnosis. In the determination of antibodies to various streptococcal exoenzymes preference is given to anti-Streptolysin O, since this sensitive parameter is found to be elevated in about 80 – 85% of cases. An international standardisation is moreover only possible in the case of ASL. As in the case of the haemolysis inhibition test, the nephelometric Latex ASL tests are standardised with the WHO Standard of the National Serum Institute, Copenhagen (1).

Since an immunological exposure of the organism to streptococcal exoenzymes is a frequent occurrence, practically all sera manifest an ASL titre. The latter depends on the age of the patient, the geographical situation and the local incidence of streptococcal infections. A single determination does not yield information on the course of the ASL levels, a relevant statement can only be made by repeating the test and comparing the results 1 to 2 weeks later.

Anti-streptococcal DNaseB antibodies are directed against the exoenzyme deoxyribonuclease B which is secreted by group A beta – haemolytic streptococci. Testing for DNaseB antibodies is important for confirming an existing or recent streptococcal infection (e.g. rheumatic fever, scarlet fever, tonsillitis, and glomerulonephritis). The antibody response to streptococcal DNaseB begins later and more strongly than the formation of antibody to streptolysin-O (1, 2). In the case of skin infections there is rarely an increase in the anti-streptolysin concentration whereas an increase is observed in the anti-streptococcal DNaseB titre (3, 5). A single result does not provide information on the presence of acute streptococcal infection and on the course of the ADNaseB concentrations, and therefore the test must be repeated after 1-2 weeks in order to enable a relevant assessment.

Reference Intervals