Circ: Practices vary greatly on follow-up for out-of-range INR values

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Prompt repeat testing after out-of-range INR [International Normalized Ratio] 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, according to research in the May issue of Circulation: Cardiovascular Quality and Outcomes. Yet, the VA study found a wide range of practice regarding the interval until a repeat test after out-of-range and mildly out-of-range INR values.

The clinical literature has demonstrated that improved control of oral anticoagulation reduces adverse events. Therefore, Adam J. Rose, MD, of the Center for Health Quality, Outcomes and Economic Research at the Bedford VA Medical Center in Bedford, Mass., and colleagues said a program of quality measurement is needed for oral anticoagulation. Therefore, in this study, they assessed the interval until the next test after an out-of-range INR value (or the “follow-up interval”) that could potentially serve as a process of care measure.

The researchers studied 104,451 patients cared for by 100 anticoagulation clinics in the Veterans Health Administration. For each site, they computed the average follow-up interval after low ( <1.5) or high ( >4.0) INR. Their outcome was each site's average anticoagulation control, measured by percent time in therapeutic range (TTR); 57 percent of the patients contributed to the low INR analysis, and 36 percent 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.

Rose and colleagues found that longer follow-up intervals were associated with worse site-level control (1.04 percent lower for each additional day). 

After a high INR, site mean follow-up interval ranged from six to 18 days, with longer follow-up intervals associated with worse site-level control (1.12 percent lower for each additional day), the researchers reported. “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,” they wrote.

“Despite being part of an integrated health system [of the VA], the 100 sites that we studied had a wide range of practice[s] in this regard, possibly due to the relative lack of evidence and clear guideline recommendations,” the authors noted. As a result, they hypothesized that clinicians practicing at each site arrive at a consensus about the ideal follow-up interval in certain situations, whether by a written or unwritten policy.

In addition to its implications for quality measurement, Rose et al said their study also has implications for clinical practice guidelines in anticoagulation care.

“Our results suggest that anticoagulation control could be improved considerably by following up within seven days after a high ( >4.0) or low ( <1.5) INR value and within 14 days after a mildly high (3.1 to 3.9) or mildly low (1.6 to 1.9) INR value,” the study authors concluded. “If all VA patients had been treated in this manner during our study, our results suggest that the VA might have recorded an overall TTR between 5 percent to 10 percent higher, a difference that has been associated with meaningful improvements in the rates of outcomes such as stroke, venous thromboembolism, major hemorrhage and mortality.”