Health Literacy and Anticoagulation-related Outcomes Among Patients Taking Warfarin

Authors

  • Margaret C. Fang MD, MPH,

    1. Division of General Internal Medicine, University of California at San Francisco, San Francisco, CA, USA
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  • Edward L. Machtinger MD,

    1. Division of General Internal Medicine, University of California at San Francisco, San Francisco, CA, USA
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  • Frances Wang MS,

    1. Primary Care Research Center, Department of Medicine, San Francisco General Hospital, University of California at San Francisco, San Francisco, CA, USA.
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  • Dean Schillinger MD

    1. Primary Care Research Center, Department of Medicine, San Francisco General Hospital, University of California at San Francisco, San Francisco, CA, USA.
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  • Preliminary results of this paper were presented during the 2004 Society of General Internal Medicine Annual meeting, Chicago, IL, USA.

  • The authors do not have any significant conflict of interests relating to this manuscript.

Address correspondence and requests for reprints to Dr. Fang: 533 Parnassus Ave., Box 0131, San Francisco, CA 94143 (e-mail: mfang@medicine.ucsf.edu).

Abstract

BACKGROUND: Little is known about whether health literacy affects anticoagulation-related outcomes.

OBJECTIVE: To assess how health literacy is associated with warfarin knowledge, adherence, and warfarin control (measured by the international normalized ratio [INR]).

DESIGN: Survey.

PARTICIPANTS: Patients taking warfarin through an anticoagulation clinic.

MEASUREMENTS: Health literacy was measured using the short-form Test of Functional Health Literacy in Adults (s-TOFHLA), dichotomized as “limited” (score 0 to 22) and “adequate” (score 23 to 36). We asked patients to answer questions relating to their warfarin therapy and used multivariable logistic regression to assess whether health literacy was associated with incorrect answers. We also assessed whether health literacy was associated with nonadherence to warfarin as well as time in therapeutic INR range.

RESULTS: Bilingual research assistants administered the survey and s-TOFHLA to 179 anticoagulated English- or Spanish-speaking patients. Limited health literacy was associated with incorrect answers to questions on warfarin's mechanism (adjusted odds ratio [OR] 4.8 [1.3 to 17.6]), side-effects (OR 6.4 [2.3 to 18.0]), medication interactions (OR 2.5 [1.1 to 5.5]), and frequency of monitoring (OR 2.7 [1.1 to 6.7]), after adjusting for age, sex, race/ethnicity, education, cognitive impairment, and years on warfarin. However, limited health literacy was not significantly associated with missing warfarin doses in 3 months (OR 0.9 [0.4 to 2.0]) nor with the proportion of person-time in therapeutic INR range (OR 1.0 [0.7 to 1.4]).

CONCLUSIONS: Limited health literacy is associated with deficits in warfarin-related knowledge but not with self-reported adherence to warfarin or INR control. Efforts should concentrate on investigating alternative means of educating patients on the management and potential risks of anticoagulation.

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