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Literacy and Numeracy Skills and Anticoagulation Control

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ABSTRACT

Background

The ability to use printed material to function in society (literacy) and to handle basic numerical concepts (numeracy) may have implications in patients’ ability to follow dosing schedules. We examined literacy and numeracy skills among patients on warfarin and explored their association with anticoagulation control.

Methods and Results

Patients older than 50 years attending two anticoagulation management units were prospectively enrolled. We measured literacy, numeracy, and international normalized ratio (INR). During a 3-month follow-up period, we calculated the variability of the INR and the amount of time a patient’s INR was within his or her therapeutic range, variables associated with bleeding and effectiveness. Among 143 patients, only 75 (52.4%) were able to read health-related words at the eighth grade level or less. Patients’ self-reported grade completed was higher than the measured literacy grade level (κ = 0.21). While 79.0% had completed at least eight grades, only 47.6% had a score at that grade level. Sixty-nine patients answered none or correctly answered fewer than two of the six numeracy questions (48.3%). The INR variability was higher among patients with lower literacy (P = 0.009) and lower numeracy skills (P = 0.004). The time in range was similar among patients at different literacy levels (P = 0.9). Patients with lower numeracy level spent more time above their therapeutic range (P = 0.04) and had a trend of less time spent in range (P = 0.10).

Conclusions

Low literacy was prevalent among study patients taking warfarin. Low literacy and numeracy were associated with measures of poor anticoagulation control.

Section snippets

Methods

We performed a prospective cohort study among patients taking warfarin. We included patients over the age of 50 attending two outpatient anticoagulation management units who had been taking warfarin for at least 1 month. One unit was university-based (staffed by a registered nurse) and the other was based at a Veterans Affairs hospital (staffed by a Doctor of Pharmacy and a registered nurse). A convenience sample of patients were recruited during their regular visits over a 7-month period

Results

During the study period, 510 patients were enlisted at the anticoagulation management units. Of those, 184 patients who were eligible for the study were approached, 143 agreed to participate (77.7%), and 41 did not agree or were excluded from the study. Patients declined to participate due to lack of time (n = 24), lack of interest (n = 9), or other reasons (n = 9) (one patient had more than one reason). The other patients in the anticoagulation units were not approached because the recruiter was not

Discussion

Low literacy was prevalent among study patients on chronic warfarin therapy; more than half were unable to read health-related words written at levels beyond the eighth grade level. Not unexpectedly, the self-reported grade completed overestimated the patients’ ability to read. In our study, patients had difficulty computing basic mathematical concepts; about half of them were unable to answer more than three mathematical questions. Most importantly, we found that a patient’s inability to read

Acknowledgments

We thank Ms. Laurin Gibson and Mrs. Amy Jackson for technical assistance and Don Holbert, PhD, for statistical assistance. We also thank Drs. Elizabeth L. McNeill, Sangnya Patel, and Gregg Talente for reviewing prior versions of this manuscript.

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    This work was supported by grant NR 04716 from the National Institute of Aging, National Institute of Nursing Research, and Office of Research on Minority Health from the Center on Minority Aging, University of North Carolina at Chapel Hill, and a Faculty Research Grant from the Brody School of Medicine at East Carolina University.

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