The Correlation between a Semi-quantitative ASO (Antistreptolysin O) Assay by Rantz-Randall and a Quantitative ASO Assay by Nephelometry

ABSTRACT

PURPOSE: Accurate diagnosis and prompt treatment of infection with Streptococcus pyogenes (group A streptococci) is required as it may cause many complications, and chronic serious sequelae, acute rheumatic fever and acute glomerulonephritis. Recently, the assay methods of ASO concentration tend to be changed into quantitatively from semi-quantitative or qualitative methods in this country. We would like to know relationships and degree of concurrences between two methods. METHODS: Total eighty-three elementary school children, aged from 7 to 8, were involved for this study. They had been examined throat swab culture with conventional methods and letting down the blood for measuring ASO titer simultaneously. We examined ASO titer by both Rantz-Randall method and Nephelometry. RESULTS: The correlation between a semi-quantitative ASO assay by Rantz-Randall (X) and a quantitative ASO assay by Nephelometry (Y) was Y=1.69X+76.7 (r=0.81). Compared to the Nephelometry test, Rantz-Randall test showed a sensitivity of 72.7% and specificity of 100%. Accordingly, the concordance rate of two methods was 89.2%. CONCLUSIONS: There seems to be high correlation and concordance rate between Rantz-Randall and Nephelometry. It needs to be changed methods for ASO titer measurement from semi-quantitative to quantitative methods for reducing possible laboratory error and for reliable standardization. Altogether, interpretation of ASO titer should be on the ASO value of different geographic areas, in different seasons, and year by year.