Annals of Clinical and Laboratory Research

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Anti Streptolysin O; Normal Values for Healthy Children Aged from 5 to 15 Years Old in Sana'a City-Yemen

Khaled AA and Hassan AA

Backgrounds: Group-A streptococcal serology is used for the diagnosis of poststreptococcal diseases, such as acute rheumatic fever, and occasionally for the diagnosis of streptococcal pharyngitis. Experts recommend that the upper limits of normal values for streptococcal serology should be determined for each individual population because of differences in the epidemiology of group A Streptococci (GAS) between these populations.

Objectives: This study was conducted firstly to determine the normal values of the upper limit of anti-streptolysin O (ASO) titer in Sana'a city. Secondly to determine the factors that might affect the levels of ASO among the selected children.

Methods: Participants with a history of GAS disease, including pharyngitis or impetigo were excluded. A total of 404 serum samples collected from children aged 5-15 years (with a sample enriched with school-aged children) were tested for the ASO titer. Reference values, including titers that were 95% of the upper limit of normal (ULN) were obtained by the calculation of 95% prediction interval (PI 95%) using a parametric method instead of the traditional non parametric approach.

Results: Normal values for the ASO titer declined in the early childhood and rose slightly in the late childhood. The estimated ASO titers that were 95% of ULN for the total was 276.2 IU/ml.

Conclusions: This study data were similar to those reported in countries with temperate climates, suggesting that a uniform upper limit of normal for streptococcal serology may be able to apply globally.