ObjectivesTo obtain systematic information on the extrinsic coagulation pathway, as well as to investigate the time course of the coagulation abnormalities in sepsis.DesignProspective observational study.SettingGeneral intensive care unit.PatientsNineteen patients with the diagnosis of severe sepsis or septic shock and nine control patients.InterventionsNone.Measurements and Main ResultsTissue factor antigen concentration (tissue factor antigen), prothrombin fragment F1+2, thrombin antithrombin III complex, fibrinopeptide A, D-dimer, and antithrombin III concentrations were measured on the day of diagnosis of severe sepsis and septic shock, and on days 1, 2, 3, and 4 after diagnosis. The concentrations of tissue factor antigen, prothrombin fragment F1+2, fibrinopeptide A, and D-dimer were significantly increased in patients with severe sepsis and septic shock compared with control subjects. However, the concentrations of thrombin antithrombin III complex showed no statistical differences between the septic patients and the control subjects. Significantly, low antithrombin III concentrations were observed in the septic patient groups compared with control subjects. With the exception of D-dimer, the concentrations of the hemostatic markers were similar between severe sepsis and septic shock patients. Significant correlations were noted between tissue factor antigen and the disseminated intravascular coagulation score (r2= .236, p < .0001) and the number of dysfunctioning organs (r2= .229, p = .035).ConclusionsWe systematically elucidated coagulation disorders in newly defined sepsis. The extrinsic coagulation pathway is activated in patients with severe sepsis and septic shock. In these patients, enhanced thrombin generation and activation, and fibrin formation were demonstrated when compared with the control subjects. Furthermore, the thrombin generated appears not to be fully neutralized by antithrombin III. (Crit Care Med 1998; 26:2005-2009)