Age-related variations in anti-streptococcal antibody levels.

The present study was undertaken to determine the upper 95% confidence limits (CL) for titres of antibodies to streptolysin O (ASO) and streptococcal DNase B (ADNB) using 741 sera from a general population. The ASO titres in sera from children increased abruptly with increasing age, from a mean of 21 (CL 67) in infants of 3 years or less to 211 (CL 462) in children 7 to 8 years old. In children 9 to 12 years of age titres exhibited a plateau with mean values of 168-258 (CL 436-611). In individuals over 20 years the mean ASO titre diminished with increasing age, individuals of 70 years or more showing a mean titre of 83 (CL 169). A similar variation was seen for ADNB. Infants 3 years of age or younger exhibited no detectable ADNB whereas individuals 70 years or more had a mean titre of 11 (CL 91). A maximal mean ADNB titre of 184 (CL 706) was detected in 9-year-old-children. It was concluded that age-related reference values for anti-streptococcal antibodies increase the clinical relevance of the tests.