Feasibility and Safety of a 12-week INR Follow-Up Protocol Over 2 Years in an Anticoagulation Clinic: A Single-Arm Prospective Cohort Study

J Thromb Thrombolysis. 2019 Feb;47(2):200-208. doi: 10.1007/s11239-018-1760-9.


The 2012 American College of Chest Physicians' guidelines recommended a 12-week INR follow-up interval may be appropriate for patients on stable warfarin doses. Limited evidence supports this recommendation. A single-arm, prospective cohort study over 24 months was completed in a Veterans Affairs anticoagulation clinic to determine the long-term feasibility and safety of implementing an extended INR follow-up interval in Veterans on stable doses of warfarin. Participants were required to have a stable warfarin dose for 6 months prior to enrollment. A prespecified protocol was used to titrate, extend, and manage the INR interval up to 12 weeks. Scheduling of extended INR intervals was a primary outcome. Safety outcomes included major and serious bleeding and thromboembolic events. A post-hoc comparison of baseline characteristics between individuals who were scheduled for at least 4 consecutive 12-week INR follow-up intervals and those who were not was completed. Of the 50 participants, 36 (72%) were scheduled for at least one 12-week interval and 15 (30%) were scheduled for 4 consecutive intervals. There were 2 thromboembolic events that occurred in 1 participant. There were 28 major and serious bleeding events in 19 participants; 8 occurred while on the extended INR interval. In the post-hoc analysis, no participants scheduled for 4 consecutive 12-week intervals had heart failure. Based on 2 years of monitoring, a 12-week INR follow-up interval using a detailed protocol with titration of INR interval extension appears feasible for a subset of patients. Patients with heart failure may not be suitable for this intervention.

Keywords: Anticoagulation; Drug monitoring; International normalized ratio; Time factors; Warfarin.

MeSH terms

  • Aged
  • Ambulatory Care Facilities*
  • Anticoagulants / administration & dosage*
  • Anticoagulants / adverse effects
  • Blood Coagulation / drug effects*
  • Drug Monitoring / methods*
  • Feasibility Studies
  • Hemorrhage / chemically induced
  • Humans
  • International Normalized Ratio*
  • Middle Aged
  • Predictive Value of Tests
  • Prospective Studies
  • Risk Factors
  • Time Factors
  • Treatment Outcome
  • United States
  • United States Department of Veterans Affairs


  • Anticoagulants