Platelet associated IgG (PAIgG) levels in 45 ITP patients were measured by the single radialimmunodiffusion (SRID) technique to determine whether PAIgG could be used as a prgnostic index for ITP. The PAIgG levels in ITP patients were significantly higher than those in normal controls and showed an inverse correlation with the platelet count (Y221.9-13.4X,p<0.01). The PAIgG level decreased significantly after the first course of steroid therapy in both the steroid responsive and the steroid resistant ITP patients. However, in the clinically stable period, the PAIgG level in the steroid resistant patients remainde significantly higher than in the responsive patients (p<0.005). Although the PAIgG level after splenectomy decreased significantly(p<0.05) in the patients with complete remission, it remained remained significantly higher (p<0.05)in the nonresponders. Maximum platelet count after therapy divided by the number of days elapsing from the time of therapy to the day showing the maximum platelet count, was significantly higher in the responders.
The PAIgG level in the stable period after steroid therapy, and the rate of increase in the platelet counts in the early period after steroid therapy were suggested to be useful as indices of the prognosis of ITP.