Determination of the upper limit of normal for serum anti-streptolysin-O titre in primary school children in Southern Nigeria; A model for other low resource settings

Abstract

The prevention and treatment of Rheumatic Heart disease is hinged on antibiotic administration in children with Group A Streptococcal (GAS) pharyngitis and Acute Rheumatic Fever (ARF). The Upper Limit of Normal (ULN) for serum Anti-streptolysin O titre (ASOT) has been employed as proof of antecedent GAS pharyngitis to fulfil the Jones’ criteria for diagnosis of ARF. This value has not been generated among West African children. Generalization of values from Caucasians (200 IU/ml) is likely to result in over-diagnosis, owing to higher GAS pharyngitis incidence in Africa. We aimed to determine the serum ASOT and its ULN in apparently healthy school-aged children in Egor Local Government Area (LGA), south-south Nigeria and to determine their relationship with socio-demographic characteristics.We recruited 384 apparently healthy school-aged pupils across eleven schools. Serum ASOT was determined by turbidimetry. Statistical analysis was done using student's t-test and Analysis of Variance (ANOVA). Level of significance was set at p < 0.05.The mean age was 8.53 ± 1.97(range 6–12) years and male-female ratio was 1.1:1. The ULN and geometric mean serum ASOT were 390.76 IU/ml and 230.04 ± 1.86 IU/ml respectively. No significant correlation was found between serum ASOT and age (r-value of −4.8%). The ULN did not vary significantly with gender, socio-economic class and the presence/absence of over-crowding in homes. The ULN for serum ASOT in apparently healthy school-aged children in Egor LGA is higher than the currently used international value. Clinicians in West Africa should consider applying higher cut-off values for the diagnosis of ARF.