The results of PAIgG assays (expressed as molecules of IgG per platelet) determined using 1 of 4 different assays for PAIgG. The assays used included a technique for measuring “total” PAIgG (first vertical column); a 2-stage assay for surface PAIgG (second vertical column); a direct binding surface assay using ¹²⁵I-staphylococcal protein A (third vertical column); and a direct binding surface assay using ¹²⁵I-monoclonal anti-IgG (fourth vertical column). Each point represents a different patient or control tested using each technique on the same day. Healthy nonthrombocytopenic controls (∆), patients with acute or convalescent immune thrombocytopenia (○), and patients with non-immune thrombocytopenia (●). Solid bar across each column, upper limits of normal, defined as 2 standard deviations above the mean PAIgG for the 29 healthy, non-thrombocytopenic controls. PAIgG, platelet-associated immunoglobulin. With permission of authors and publishers.³⁶