Objective: To determine age-specific upper limit of normal (ULN) values of the ASO and ADB titres in children aged 4-14 years in urban Melbourne. Serology is often used to diagnose a preceding Streptococcus pyogenes infection, particularly in potential cases of rheumatic fever and post-streptococcal glomerulonephritis. The most commonly used antigens are antistreptolysin O (ASO) and antideoxyribonuclease B (ADB). Reference ranges used in Australia for these serological markers are usually based on data in adults from other countries. There are no age-specific reference values for Australian children.
Methods: Sixty-six sera from children with no history of recent streptococcal infection were obtained in May-June 2002. The children were divided into three age groups for analysis: 4-5 (n = 20), 6-9 (n = 19) and 10-14 (n = 25) years. The geometric mean titre and ULN (defined as the 80th percentile) for the ASO and ADB titres for each age group were determined in both international and log units.
Results: The ULN for ASO titres in each age group was 120 (2.08 log units), 480 (2.68) and 320 (2.51). The ULN for ADB titres in each age group was 100 (2.00 log units), 400 (2.60) and 380 (2.58).
Conclusion: The ASO and ADB ULN values in school-aged children are higher than the current reference ranges suggest.