Elevated platelet-associated IgG in the thrombocytopenia of septicemia

The mechanism of thrombocytopenia, a frequent complication of septicemia, is obscure, but indirect evidence suggests that the immune system may be involved. To investigate this possibility, we quantitated platelet-associated IgG on platelets obtained from 44 patients during 46 episodes of septicemia. Thrombocytopenia occurred in 21 of 46 episodes (46 per cent). Platelet-associated IgG was elevated in eight of 11 episodes of gram-negative septicemia and thrombocytopenia (47.3 +/- 11.7 fg of IgG per platelet [mean +/- S.E.]) and in one of 20 patients with gram-negative septicemia and normal platelet counts (5.9 +/- 1.1) (P less than 0.001). Elevated levels occurred in eight of 10 patients with gram-positive septicemia and thrombocytopenia (55.3 +/- 14.7 fg of IgG per platelet) and in none of 11 patients with gram-positive septicemia and normal platelet counts (5.6 +/- 1.7) (P less than 0.001). Serial testing during the thrombocytopenia and recovery showed an inverse relation between the platelet count and platelet-associated IgG. Thrombocytopenia in some patients with septicemia may be related to the binding of IgG to platelets.