Disclosed are devices for collecting blood that contain an anti-coagulant and an additive that delays clotting by inhibiting the contact pathway for thrombin generation. The additive is a coagulation contact pathway inhibitor additive that is at least one of a Factor XI inhibitor, a Factor XII inhibitor, a kallikrein inhibitor and combinations thereof, each in an amount effective to mediate or suppress the contact pathway for thrombin generation. Methods of making and using the devices, and kits containing the devices, are also provided.
