Over diagnosis of
acute rheumatic fever (ARF) based on a raised
antistreptolysin O titer (ASOT) is not uncommon in endemic areas. In this study, 660 children (aged 9.2 ±1.7 years) were recruited consecutively and classified as: G1 (control group, n=200 healthy children), G2 (n=20 with ARF 1(st) attack), G3 (n=40 with recurrent ARF), G4 (n=100 with
rheumatic heart disease (RHD) on long acting
penicillin (LAP)), G5 (n=100 with acute follicular
tonsillitis), and G6 (n=200 healthy children with history of repeated follicular
tonsillitis more than three times a year). Serum ASOT was measured by
latex agglutination. Upper limit of normal (ULN) ASOT (80(th) percentile) was 400 IU in G1, 200 IU in G4, and 1600 IU in G6. Significantly high levels were seen in ARF 1st attack when compared to groups 1 and 5 (P<0.001 and P<0.05, respectively). ASOT was significantly high in children over ten years of age, during winter and in those with acute rheumatic
carditis. ASOT showed significant direct correlation with the number of attacks of
tonsillitis (P<0.05). Egyptian children have high ULN ASOT reaching 400 IU. This has to be taken into consideration when interpreting its values in suspected ARF. A rise in ASOT is less prominent in recurrent ARF compared to 1st attack, and acute and recurrent
tonsillitis. Basal levels of ASOT increase with age but the pattern of increase during
infection is not age dependent.