Improving Anticoagulation Measurement Novel Warfarin Composite Measure

Area of Science:

• Pharmacology
• Clinical Medicine
• Health Services Research

Background:

• Percent time in therapeutic range (TTR) and international normalized ratio (INR) variability are independent measures of warfarin control.
• Both TTR and INR variability are associated with patient outcomes.
• The current measures have limitations in assessing overall warfarin control and patient risk.

Purpose of the Study:

• To examine the advantages of a warfarin composite measure (WCM) for assessing patient outcomes.
• To determine how WCM compares to TTR and INR variability in predicting warfarin-related complications.
• To evaluate the impact of different warfarin control measures on anticoagulation clinic performance rankings.

Main Methods:

• A warfarin composite measure (WCM) was constructed by equally weighting standardized TTR and standardized log-transformed INR variability.
• Data from 103,897 warfarin-experienced patients across 100 anticoagulation clinics were used.
• Associations between WCM, TTR, INR variability, and outcomes (ischemic stroke, major bleeding, fatal bleeding) were analyzed in a subset of 40,404 patients with atrial fibrillation.

Main Results:

• WCM demonstrated the largest difference in hazard ratios for stroke and fatal bleeding between excellent and poorest control quintiles compared to TTR or log INR variability alone.
• The WCM did not show a significantly larger range for major bleeding compared to its components.
• Clinic performance rankings shifted considerably depending on whether TTR, INR variability, or WCM was used, with moderate agreement between WCM and its components, but weak agreement between TTR and INR variability.

Conclusions:

• WCM provides a broader assessment of warfarin-related risk, overcoming limitations of TTR and INR variability used separately.
• The choice of anticoagulation measure significantly impacts the performance evaluation of anticoagulation clinics.
• WCM offers a more comprehensive approach to evaluating warfarin control and patient outcomes.