There are many overused tests in the vastness of medicine, but few synthesize both overuse and inappropriateness like the international normalized ratio (INR). The INR is a test with a singular purpose: a standardized calibration for the measurement of the anticoagulant activity of warfarin. It has no other reason for existence, yet it is frequently ordered as part of routine screening for previously undiagnosed coagulopathy. Indeed, its use is so prevalent as a stowaway in anachronistic order sets that ACEP once considered tracking coagulation studies as a marker of low-quality care.1 The INR and its related cousin prothrombin time (PT) are elevated only in a handful of conditions: vitamin K–dependent factor deficiency, presence of factor VII inhibitor, disseminated intravascular coagulation, or in the setting of massive transfusion. An incidentally encountered mild elevation of INR or PT is typically of no clinical significance nor is it associated with increased bleeding risk.
Explore This IssueACEP Now: Vol 35 – No 10 – October 2016
The prime example of this misunderstanding and misuse of the INR is in our approach to patients with cirrhosis or end-stage liver disease (ESLD). As a result of their chronic liver injury, these patients have impaired intrahepatic synthesis of a number of important elements of hemostasis. Further complicating the matter, much of our contact with patients suffering from ESLD occurs in the heat of critical illness such as upper gastrointestinal bleeding, including brisk variceal bleeding. This is, unfortunately, where the INR does us the greatest disservice.
The INR does not accurately reflect underlying coagulopathy. Patients with impaired hepatic synthetic dysfunction and ESLD do suffer from a diminished hemostatic reserve (ie, thrombocytopenia, low levels of coagulation factors, and dysfibrinogenemia).2 However, these deficiencies are counterbalanced by pro-hemostatic features (ie, elevated levels of von Willenbrand factor, elevated factor VIII, and low levels of protein C and S). The PT and INR only narrowly reflect one portion of the coagulation cascade, do not reflect a holistic view of the ability to clot, and do not accurately represent bleeding risk.
In fact, at one surgical center, the authors report on a series of 500 consecutive liver transplant procedures performed in the setting of advanced liver disease.3 The mean INR for these patients was 1.8. In spite of this, these authors were able to perform 398 of the 500 surgical procedures without requiring transfusion of any additional blood products and, similarly, without any prophylactic administration of fresh frozen plasma (FFP). In fact, when these authors were designing their surgical protocol for liver transplant, their retrospective case review revealed administration of FFP was actually a risk factor for red blood cell (RBC) transfusion and decreased one-year survival rates. This leads to a second important conclusion regarding the approach to patients with ESLD: FFP should not routinely be used as procedural prophylaxis or treatment for the bleeding cirrhotic with an elevated INR.