The Association of Health Literacy With Time in Therapeutic Range for Patients on Warfarin Therapy

Abstract

Patients on warfarin therapy need to achieve and maintain anticoagulation control in order to experience the benefits of treatment while minimizing bleeding risk. Low health literacy skills may hinder patients' ability to use and adhere to warfarin in a safe and effective manner. The authors conducted this study to evaluate the relationship between health literacy and anticoagulation control among patients on chronic warfarin therapy. Participants were recruited from 2 diverse anticoagulation clinics in North Carolina. Time in therapeutic range (TTR) for warfarin therapy was used as a measure of anticoagulation control. Health literacy was assessed using the short form of the Test of Functional Health Literacy in Adults (S-TOFHLA). Of the 198 study participants, 51% had limited health literacy (S-TOFHLA score of 0–90) and 33% had poor anticoagulation control (TTR <50%). Participants with limited health literacy were less likely to correctly answer warfarin-related knowledge questions. Limited health literacy was significantly associated with TTR <50% (adjusted odds ratio = 2.34, 95% CI [1.01, 5.46]). Findings indicate that limited health literacy is associated with poor anticoagulation control for patients on warfarin therapy. Lack of medication understanding may hinder the safe and effective use of this narrow therapeutic index drug.

Acknowledgments

This study was presented in part at the 5th Annual Health Literacy Research Conference (HARC V), which was held on October 28–29, 2013, in Washington, DC. The authors thank Marguerite Conger, Emily Eddy, Rupal Kasbekar, Krista Luck, Brooke McGuirt, Heather Moore, Patty Riddle, Tara Strigo, Susan Sutherland, and Cheryl Wisseh for their assistance with this study.

Notes

^a p value for Student's t test (age), Mann-Whitney U test (number of tablet strengths), chi-square (female, working for pay, income, clinic location), or Fisher's exact test (race/ethnicity, insurance, education level).

^b For no. of tablet strengths, limited health literacy n = 92, adequate health literacy n = 97.

^a For Question 1, Fisher's exact test was used; for Questions 2–4, chi-square analysis was used.

^a Adjusted for age, race, gender, education, income, number of tablets, and health literacy.