Anti-streptococcal antibodies in the diagnosis of acute and post-streptococcal disease: streptokinase versus streptolysin O and deoxyribonuclease B

Aims: To establish population normal values and compare the diagnostic value of antibodies against streptokinase ( ASK), streptolysin O (ASO) and deoxyribonuclease B (ADNaseB) singularly and in combinations in acute and post-streptococcal disease. Methods: A retrospective analysis of serological results was performed to define population norms. Subjects with acute culture-confirmed infection and post-streptococcal disease were assessed using population norms, as were matched controls. The sensitivity and specificity of each antibody assay and of combinations of the different assays were calculated. Results: Age specific population normal values were derived from 2321 specimens. None of the three antibodies alone or in combination was a reliable marker of acute streptococcal infection. The sensitivity and specificity of a single antibody titre in post-streptococcal disease ranged from 70.5 to 72.7% and 86.4 to 93.2%, respectively. The combination of ASO and ADNaseB was the most sensitive and specific combination for identifying post-streptococcal disease ( sensitivity 95.5%, specificity 88.6%). Conclusions: In the diagnosis of acute and post-streptococcal disease, the addition of ASK does not increase the sensitivity or specificity of serological testing. A combination of ASO and ADNaseB is required in post-streptococcal disease to achieve maximum sensitivity and specificity.