Quantitative evaluation of variation in composition of the streptozyme agglutination reagent for detection of antibodies to group A streptococcal extracellular antigens.

The antibody titers of 90 acute- and convalescent-phase sera from 30 patients (mean age, 15.0 years) were studied with five different lots of Streptozyme reagent to determine whether variation exists among lots of reagent and whether this can affect clinical interpretation of antibody titers. Each serum was tested simultaneously with each of the five lots of reagent. Lot-to-lot variation in the reagent resulted in a significant difference (greater than 2 dilution increments) in antibody titer for 61 (68%) of the 90 sera tested. In addition, differences among the five lots also resulted in variation in determining whether a significant rise in titer occurred from the acute-phase to the convalescent serum for a given patient. These data indicate a need for precise identification and quantitation of the streptococcal antigens coated onto erythrocytes used for the Streptozyme test reagent.