New hemolytic method for determination of antistreptolysin O in whole blood.

A new method is proposed for the determination of antistreptolysin O, based on the properties of streptolysin O. The reduced form of the toxin is hemolytic, whereas the oxidized form is not; this activity can be restored, however, by a reducing agent. Both forms maintain the capacity to bind specific antibodies. Unlike the classical method, the assay is performed on whole blood, using the patient's own erythrocytes as revealing agents. A procedure is proposed which limits the operation to a single dilution of a microvolume of blood (0.05 ml brought to 2 ml) and to the distribution of constant quantities in test tubes prefilled with different amounts of oxidized streptolysin O. After a few minutes, a reducing agent is added, and the reading is performed as in the classical technique after sedimentation of the erythrocytes. Correlation with the traditional method (r = 0.987) is evaluated on the basis of the results of samples from hospitalized patients.