Theoretical relationship between concentration of coagulation factors and PT/INR. Based on the experience with single factor deficiencies, coagulation proceeds normally until the concentration of factors drops below 30%. Thus there is a significant reserve of clotting factors (the physiologic reserve). Also note that abnormal clotting times can occur while the levels of clotting factors are still within the physiologic reserve, another reason why the PT/INR does not necessarily predict peri-operative bleeding. Refer to text for explanation of the labels. Modified and reprinted from reference [23], with permission from the AABB.

PT values in healthy individuals who first received oral anticoagulation, then 1 L of autologous plasma, then oral vitamin K at the end of the study. Note how the FFP produced only a partial correction of the elevated PT (B) while the vitamin K completely reversed the coagulopathy (D). The therapeutic effect of FFP lasted for approximately 7-8 hours (C). Refer to text for explanation of the labels. Modified and reprinted with permission from the AABB from reference [19]. ◇ (green line), mean test infusion; × (purple dotted line), mean control infusion; bars represent 95% CIs.

Theoretical response to plasma transfusion based on a formula derived from a clinical study of 140 adult plasma recipients [28]. The main predictor of the response to plasma transfusion is the pretransfusion INR.