A simplified radioimmunoassay for antibodies causing immune cytopenia

A two-step, solid-phase radioimmunoassay for the measurement of antibodies directed against platelets, neutrophils, and red blood cells is described. Cells to be tested or standard solutions of human IgG (HIgG) first are incubated with excess 125I goat anti-human IgG. Unbound 125I anti-IgG is adsorbed in a second step to polystyrene balls (PB) coated with excess human IgG. Inhibition of binding in this second step is related directly to the level of cell associated IgG. The amount of cell bound IgG is determined by comparison to a inhibition curve for standard IgG solution. The method was evaluated by quantitating antibody levels in patients with clinical evidence of immune cytopenias.