A rapid turbidimetric immunoassay for serum antistreptolysin-O

We designed a rapid, quantitative turbidimetric immunoassay for serum antistreptolysin-O (ASO), based on the immunoprecipitating velocity with purified streptolysin-O (SLO), which can be measured turbidimetrically at 340 nm. The assay system involves polyoxyethylene mono-p-nonylphenyl ether to accelerate and enhance the immunoprecipitation reaction. No antibody excess phenomenon is observed, up to 1,700 U/ml. Grossly icteric sera can be assayed. Patient sera gave acceptable results. Free cholesterol offers no interference. The standard curve is linear for values up to 800 U/ml. Results measured by the proposed method and those by the conventional microtitration method correlated well. Analytical recovery averaged 90.1% (80.3%-102.5%). Within-run and day-to-day CVs ranged from 2.1% to 3.5% and from 2.5% to 6.9%, respectively. Working SLO is stable for at least 15 days at 4 degrees C. The proposed method has proven to be superior to other available methods for measuring serum ASO.