Incidence of autoantibodies to GPIIb/IIIa in chronic autoimmune thrombocytopenic purpura may be overestimated by the MAIPA.

Twenty-one serum samples from patients with thrombocytopenia and five from normal individuals were analysed by the MAIPA test to determine specificity of autoantibody reactivity against platelet glycoprotein IIb/IIIa using murine monoclonal antibodies. The sera were also analysed by dot blot to determine their anti-murine IgG activity. Two of the three patient samples positive in the MAIPA test were positive in the dot blot test for anti-murine IgG activity, and on repeating the MAIPA following preabsorption of the serum with mouse ascites proteins they gave negative results. Reactivity of the sample which did not correct by this procedure was shown to be due to an antiHPA1a alloantibody. The potential problem of human heterophile antibodies reacting with mouse antibodies in the MAIPA has been identified and a modification which corrects this has been demonstrated.