A simple and rapid method to detect platelet associated IgG.

In order to measure platelet associated IgG (PAIgG), a semiquantitative method was devised, utilizing the ability of staphylococcal protein A (SpA) to bind human IgG specifically. Platelets bound to sheep red blood cells coated with SpA were separated from non-bound platelets by centrifugation through Ficol-paque solution and an adhesive percentage (Binding Rate) was calculated by enumeration of platelets remaining in an upper phase. In a total of 72 cases including 15 cases of idiopathic thrombocytopenic purpura (ITP), PAIgG was studied, using this new method and quantitative Fab, anti-Fab assay. Binding Rate was 9.3 +/- 3.8% in normal subjects and 26.5 +/- 10% in ITP patients, which difference was statistically significant (p less than 0.01). A good correlation was observed between Binding Rate and peripheral platelet count in ITP (r = 0.7299, p less than 0.01) and also between Binding Rate and values of PAIgG by Fab, anti-Fab assay (r = 0.8309, p less than 0.01). These results indicate that this new method is reliable to detect PAIgG in addition to its simplicity and rapidity.