Prompt Repeat Testing After Out-of-Range INR Values

Abstract

Background— Improved control of oral anticoagulation reduces adverse events. A program of quality measurement is needed for oral anticoagulation. The interval until the next test after an out-of-range International Normalized Ratio (INR) value (the “follow-up interval”) could serve as a process of care measure. Methods and Results— We studied 104 451 patients cared for by 100 anticoagulation clinics in the Veterans Health Administration (VA). For each site, we computed the average follow-up interval after low (≤1.5) or high (≥4.0) INR. Our outcome was each site's average anticoagulation control, measured by percent time in therapeutic range (TTR); 59 837 patients (57%) contributed to the low INR analysis, 37 697 (36%) contributed to the high INR analysis, and all patients contributed to the dependent variable (mean site TTR). After a low INR, site mean follow-up interval ranged from 10 to 24 days. Longer follow-up intervals were associated with worse site-level control (1.04% lower for each additional day, P <0.001). After a high INR, site mean follow-up interval ranged from 6 to 18 days, with longer follow-up intervals associated with worse site-level control (1.12% lower for each additional day, P <0.001). These relationships were somewhat attenuated but still highly statistically significant when the proportion of INR values in-range was used as the dependent variable rather than TTR. Conclusions— Prompt repeat testing after out-of-range INR values is associated with better anticoagulation control at the site level and could be an important part of a quality improvement effort for oral anticoagulation.