NEW YORK - A novel warfarin composite measure (WCM) that combines percent time in therapeutic range (TTR) and international normalized ratio (INR) variability might be useful in comparing anticoagulation clinic performance rankings, researchers report.
TTR reflects the intensity of anticoagulation, whereas INR variability reflects its stability. Both are important measures of anticoagulation quality, and previous studies have suggested their combination provides added value.
Dr. Zayd Razouki from Durham VA Medical Center in North Carolina and colleagues developed the WCM, which combines standardized TTR and standardized log INR variability, and examined its feasibility for profiling anticoagulation clinics in the Veterans Health Administration.
WCM's hazard ratios for fatal bleeding and ischemic stroke were greater with very poor control or poor control, compared with those with TTR or INR variability, the researchers report in Circulation Cardiovascular Quality and Outcomes, online September 29.
In contrast, WCM's hazard ratios for major bleeding were larger than those with INR variability but not significantly different from those with TTR.
As for patient level outcomes, WCM was no better than TTR or INR variability.
At the anticoagulation clinic level, WCM reconciled moderately well the discordance in rankings that occurred when using TTR or INR variability separately.
"We would recommend the use of WCM as a performance measure for clinic profiling, as it seems to identify different clinics as outliers," the researchers conclude. "Both on an empirical and a theoretical basis, WCM captures more completely relevant dimensions of anticoagulation control than its component measures."
Dr. Gabriel Vanerio from CASMU Arrhythmia Service in Montevideo, Uruguay, recently demonstrated the usefulness of INR variability for assessing anticoagulation quality. While admitting that the WCM is "very well constructed," he said by email, "I do not believe that this new measurement will be clinically useful."
Instead, Dr. Vanerio suggested that physicians should take home "the importance of anticoagulation quality control" as the main message of this report.
Dr. Razouki did not respond to a request for comments.