Less common assays used to detect anti-platelet glycoprotein autoantibodies in patients with ITP. Immunoblotting is an indirect assay in which normal platelet proteins are separated and then mixed with patient test plasma. Labeled anti-human antibody detects the autoantibody and the molecular weight of the glycoprotein determines the specificity of the autoantibody. Immunoprecipitation can be direct or indirect. For direct immunoprecipitation, patient test platelets are labeled and lysed, and the suspected autoantibody is bound to the labeled glycoprotein. In the indirect assay, normal platelets are sensitized with patient test plasma before lysis. Autoantibody–glycoprotein complexes are immunoprecipitated, separated, and autoradiographed to identify the glycoproteins by molecular weight.