Prothrombin time (PT) is widely utilized for evaluation of diseases with single or multiple coagulation factors disorders, such as severe liver dysfunction and disseminated intravascular coagulation (DIC). However, its standardization of reagent and method is not established yet for universal purpose except International Normalized Ratio (INR) for control of oral anticoagulant therapy (OAT). Neither Prothrombin time ratio adapted in Japanese criteria for DIC nor seconds method in criteria reported by the last SSC meeting is corrected between assays, therefore much dependence on these criteria causes risk of misdiagnosis. In order to resolve incoherence of method of PT, we performed this study for introducing INR method to diagnostic criteria for DIC. In our results, sensitivities of two reagents from human tissue factor (TF) to DIC model plasma with middle to low activities of multiple coagulation factors almost equal to plasma from patients with OAC, although other two reagents from rabbit TF show discrepancy of sensitivities between DIC and OAT plasma. These suggest a potentiality to introduce INR system to diagnosis of DIC when human TF is used as a PT reagent. Based on standardization of method, significance of PT in DIC criteria should be reevaluated in worldwide.