Elevated Platelet Antibodies in Septicemic Thrombocytopenia

Thrombocytopenia often complicates bacterial septicemia in the absence of evidence of DIC. Evidence is provided that thrombocytopenia in these patients is caused by adsorption of IgG to platelets (immune thrombocytopenia) which occurs either as a consequence of bacterial injury or adsorption of immune complexes consisting of bacteria or bacterial products and their specific antibodies. Platelet associated IgG (PAIgG) (assayed by inhibition of lysis) was determined in 44 patients with bacterial septicemia. PAIgG was elevated in 8 of 11 thrombocytopenic patients with gram negative septicemia (mean 47 tg IgG/platelet, p<0.0001), 8 of 10 thrombocytopenic gram positive septicemic patients (mean 55 fg IgG/platelet, p<0.0001) and in one of the 31 septicemic patients with normal platelet count (mean 5 fg IgG/platelet). In vitro studies of serum and platelets obtained after 2 patients had recovered demonstrated that PAIgG was elevated to 100 fg IgG/ platelet when their respective bacteria were incubated first with their serum and then with their platelets. In contrast, when bacteria were added to the platelets before Incubation with serum, there was only a slight elevation in PAIgG. Results indicate that PAIgG is frequently elevated In septicemic patients with thrombocytopenia and that in some of these patients the thrombocytopenia is caused by adsorption of immune complexes to the platelets.