Journal of General Internal Medicine

, Volume 21, Issue 8, pp 841–846 | Cite as

Health literacy and anticoagulation-related outcomes among patients taking warfarin

  • Margaret C. FangEmail author
  • Edward L. Machtinger
  • Frances Wang
  • Dean Schillinger
Original Articles


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 (OR6.4 [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.

Key words

health literacy anticoagulation knowledge adherence 


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Copyright information

© Society of General Internal Medicine 2006

Authors and Affiliations

  • Margaret C. Fang
    • 1
    Email author
  • Edward L. Machtinger
    • 1
  • Frances Wang
    • 2
  • Dean Schillinger
    • 2
  1. 1.Division of General Internal MedicineUniversity of California at San FranciscoSan FranciscoUSA
  2. 2.Primary Care Research Center, Department of Medicine, San Francisco General HospitalUniversity of California at San FranciscoSan FranciscoUSA

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