Annual changes of upper limit of ASO titer in school children

ASO titers of school children were studied during a period from 1975 to 1981, and the annual difference of this titer was investigated. As reported by many authors, the upper limit of normal ASO titer was 250 units and values of 333 units or more should be considered abnormal in our series of children, because 15 to 20% of the population had an antibody titer of 333 units or more. The upper limit of the normal titer was the highest in 1975 when 19.7% of the children showed more than 500 units, and the lowest in 1980 when 20.1% of the children showed more than 80 units. Thus, there was a six-dilution difference in the normal upper limit between these 2 years. We must consider the annual changes of the normal upper limit of streptococcal antibody titer in order to make an accurate diagnosis.