How Rapidly Does INR Decrease?

Here is a question that came to me from the American Society for Clinical Laboratory Science Consumer Web Forum:

How quickly will an elevated international normalized ratio (INR, PT/INR) decrease/time? I appreciate the answer may be “it depends,” but for patients on warfarin and with an elevated INR (for example 4.0 in a patient with and INR goal of 2.0–3.0) how quickly can we expect an INR to decrease per day when warfarin is stopped? The stopping rule for a procedure encourages stopping warfarin five days before a procedure, suggesting a decrease in INR of ~0.5/day when warfarin is held.

Hello, and thank you for your question. No one has published a prospective controlled study to determine an empiric timeline, however it is reasonable to predict an interval based on the average half-lives of the vitamin K-dependent coagulation factors II, VII, IX, and X. X and II are the longest at 52 and 60 hours, respectively, so the prothrombin time (PT) in seconds should drop to halfway between peak and normal in about 3.5 days. The INR could then be computed from the PT in seconds, and should come out to roughly the midpoint between the peak and 1.0. This is supported by Francis, CS. Chapter 26, Antithrombotic Agents, in Kitchens CS, Alving B, Kessler CM, Consultative Hemostasis and Thrombosis, 2nd edition, 2007, Elsevier, who state, “Hold warfarin 4 to 5 days and check the INR one day before surgery and perform surgery if it is 1.5 or less.” I hope this helps, and if any of our subscribers have additional experience or information, please comment.