الفهرس 
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Abstract
Antistreptolysin O (ASO) titer is a blood test to measure antibodies against strepolysin O, a substance produced by group A Streptococcus bacteria. ASO particularly useful for the diagnosis of acute rheumatic fever and acute post streptococcal glomerulonephritis.
Acute rheumatic fever is an autoimmune disease that follows infection with group A Streptococci (GAS); however, the isolation of GAS is uncommon (< 15%), and so confirmation of the diagnosis often relies on streptococcal antibody tests.
Streptococcal titers vary according to a number of factors, including age and population. In developed countries, where impetigo caused by GAS is uncommon, streptococcal titers in the population primarily reflect the incidence of pharyngeal infection with GAS; therefore, the titers in healthy people are low in early childhood, rise to a peak in children aged 5 to 15 years, decrease in late adolescence and early adulthood, and then flatten off after that.
Because of these differences in titers with age, it is recommended that age-stratified upper-limit-of-normal values be determined for populations of interest by testing people who have not had a recent streptococcal infection.
The ASO titer tends to rise a week following infection, peaks at 3 to 5 weeks, and begins to decline after 8 weeks; and it responds more vigorously to pharyngeal infection than skin infection. The Anti-DNase B (ADB) titer peaks at 6 to 8 weeks after infection and begins to decline at 12 weeks, and it responds vigorously to both pharyngeal and skin infections. Therefore, subjects with recent pharyngitis or skin infections should not be included in the sample. The exclusion of children with GAS throat carriage is not necessary, as all healthy pediatric populations include carriers of GAS.
The aim of this study was to determine upper limit of normal range of anti streptolysin O titer in normal healthy school age children from 6-15 years old in Menoufia Governorate using latex agglutination method.
This cross-sectional prospective study was carried out in Menoufia Governorate. The study was conducted on rural and urban school children (three rural and three urban schools at Ashmoun, Menouf and El Bagour). The collected sample was tested in Clinical Pathology Laboratory at Menoufia University Hospitals in the period from September 2018 to April 2019.
Four thousands children aged 6-15 years participated in this study after consent from their parents. This systemic random sample was taken from Outpatient Clinics in Menoufia University Hospitals from cases coming for causes other than infection and from school children.
All children were subjected to: full medical history, full clinical examination (chest, cardiac, abdominal, throat and skin examinations) and investigation including CBC, ESR and ASOT.
The studied children showed age ranged from 6 to 15 years. Children aged 6 and 7 years represented the highest percentages 17.8% and 17.8% respectively. Males represented 48.8% while females represented 51.2%. Rural children were 50.6% while urbans were 49.4%. Younger children (6 to 10 years) were 60.4%, while older children (more than 10 years) were 39.6%. Mann-Whitney test was conducted and showed a non-significant relationship between age categories and ASOT. Male had lower ASO titer than female with no significant relationship.
Rural children had higher ASO titer than urban children with no significant relationship. ASO titer ranged from 75 IU to 475 IU. Specificity of ASO titer in diagnosis of rheumatic fever was determined and found that for ASO titer 200, specificity will be 67%. For ASO titer 300, specificity will be 80%. For ASO titer 375, specificity will be 90%.
We found that the mean titer of ASO in children over 10 years of age (182.1 IU/ml) and we found that the mean titer of ASO in children aged 6-10 years was (188.5 IU/ml).
Although the correlations were statistically insignificant , younger children had a higher ASO titer than older children.
Our study showed that ULN of ASOT in normal Egyptian children is quite high, and may reach up to 475 IU/ml. Although the levels were high, they did not warrant any further investigations or treatment since these children were normal and had no complaint at the time of sampling. Re-infection usually results in sustained or continuously rising titers. Therefore, an isolated high ASOT is not sufficient to diagnose ARF.