Antistreptolysin-O: its interaction with streptolysin-O, its titration and a comparison of some standard preparations.

The quantitative determination of antistreptolysin-O in the serum of a patient is frequently used as an aid in the presumptive diagnosis of a recent streptococcal infection. Difficulties have been experienced in obtaining consistently reproducible results, when large numbers of sera are tested, with accurate titration methods simple enough to be used routinely in a serological laboratory.An investigation of the streptolysin-antistreptolysin reaction has revealed that the time of interaction at 37 degrees C routinely in use in this test is very critical. Results are presented suggesting that this critical effect is due to the instability of the toxin, which is possibly attacked by the active proteinase present in streptolysin preparations. It was possible to develop a modified method using twofold dilutions of serum and a 50% haemolysis endpoint under conditions where proteinase has little effect on the toxin. This method has proved satisfactory in routine laboratory use with large numbers of sera.A quantitative comparison of various standard antistreptolysin preparations available throughout the world revealed a reasonable constancy of absolute value when compared with the original Todd standard. Differences in their neutralization reactions with streptolysin-O were, however, apparent.