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Original Research: ANTITHROMBOTIC THERAPY |

Can We Predict Daily Adherence to Warfarin?: Results From the International Normalized Ratio Adherence and Genetics (IN-RANGE) Study

Alec B. Platt, MD, MSCE; A. Russell Localio, PhD; Colleen M. Brensinger, MS; Dean G. Cruess, PhD; Jason D. Christie, MD, MSCE, FCCP; Robert Gross, MD, MSCE; Catherine S. Parker, MD, MS; Maureen Price, RN; Joshua P. Metlay, MD, PhD; Abigail Cohen, PhD; Craig W. Newcomb, MAR; Brian L. Strom, MD, MPH; Mitchell S. Laskin, RPh; Stephen E. Kimmel, MD, MSCE
Author and Funding Information

From the Center for Health Equity Research and Promotion (Dr Platt) and (Drs Gross and Metlay), Philadelphia Veterans Affairs Medical Center, Philadelphia, PA; the Reading Hospital and Medical Center (Dr Platt), Reading, PA; the Center for Clinical Epidemiology and Biostatistics, Department of Biostatistics and Epidemiology (Drs Localio, Christie, Gross, Metlay, Cohen, Strom, and Kimmel, Mss Brensinger and Price, and Mr Newcomb) and Department of Medicine (Drs Christie, Gross, Metlay, and Strom), University of Pennsylvania School of Medicine, Philadelphia, PA; the Center for Education and Research on Therapeutics (Drs Localio, Gross, Metlay, and Strom), University of Pennsylvania, Philadelphia, PA; the Department of Psychology (Dr Cruess), University of Connecticut, Storrs, CT; the Department of Internal Medicine (Dr Parker), Beth Israel Deaconess Medical Center, Boston, MA; and the Department of Pharmacy Service (Mr Laskin), Hospital of the University of Pennsylvania, Philadelphia, PA.

Correspondence to: Stephen E. Kimmel, MD, MSCE, University of Pennsylvania School of Medicine, 707 Blockley Hall, 423 Guardian Dr, Philadelphia, PA 19104-6021; e-mail: stevek@mail.med.upenn.edu


Funding/Support: The IN-RANGE study was supported by grants from the National Institutes of Health[R01-HL66176] and the Agency for Health Research and Quality [P01-HS11530]. Dr Kimmel was also supported by P20RR020741 and K24HL070936.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestpubs.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;137(4):883-889. doi:10.1378/chest.09-0039
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Background:  Warfarin is the primary therapy to prevent stroke and venous thromboembolism. Significant periods of nonadherence frequently go unreported by patients and undetected by providers. Currently, no comprehensive screening tool exists to help providers assess the risk of nonadherence at the time of initiation of warfarin therapy.

Methods:  This article reports on a prospective cohort study of adults initiating warfarin therapy at two anticoagulation clinics (university- and Veterans Affairs-affiliated). Nonadherence, defined by failure to record a correct daily pill bottle opening, was measured daily by electronic pill cap monitoring. A multivariable logistic regression model was used to develop a point system to predict daily nonadherence to warfarin.

Results:  We followed 114 subjects for a median of 141 days. Median nonadherence of the participants was 14.4% (interquartile range [IQR], 5.8-33.8). A point system, based on nine demographic, clinical, and psychosocial factors, distinguished those demonstrating low vs high levels of nonadherence: four points or fewer, median nonadherence 5.8% (IQR, 2.3-14.1); five points, 9.1% (IQR, 5.9-28.6); six points, 14.5% (IQR, 7.1-24.1); seven points, 14.7% (IQR, 7.0-34.7); and eight points or more, 29.3% (IQR, 15.5-41.9). The model produces a c-statistic of 0.66 (95% CI, 0.61-0.71), suggesting modest discriminating ability to predict day-level warfarin nonadherence.

Conclusions:  Poor adherence to warfarin is common. A screening tool based on nine demographic, clinical, and psychosocial factors, if further validated in other patient populations, may help to identify groups of patients at lower risk for nonadherence so that intensified efforts at increased monitoring and intervention can be focused on higher-risk patients.

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