Functional Health Literacy and the Risk of Hospital Admission Among Medicare Managed Care Enrollees

METHODS

Patient enrollment and data collection for this study have been described in detail previously.6 New Medicare enrollees in health plans of a national managed care organization in 4 US cities (Cleveland, Ohio; Houston, Tex; Tampa, Fla; and Ft Lauderdale–Miami, Fla) were eligible to participate. Three months after enrollment, a letter of introduction describing the study and how confidential information collected during this study would be handled was sent to each member who was at least 65 years of age. One week later, interviewers called each enrollee to determine eligibility. Individuals who indicated that they were not comfortable speaking either English or Spanish; were blind or had a severe vision problem that could not be corrected with glasses; or did not know what year or month it was, what state they lived in, what year they were born, or their address were ineligible.

RESULTS

A total of 7471 enrollees were contacted by telephone 3 months after they enrolled in the managed care plan. Of these, 3390 refused to participate, 737 did not meet eligibility criteria, and 3344 completed the in-home interview. A total of 84 individuals were excluded because they did not complete the short version of the Test of Functional Health Literacy in Adults, leaving 3260 participants available for analysis. Nonresponders were more likely to be aged 85 or older (7.5% vs 5.4%) and more likely to be male (45.2% vs 42.6%). Nonresponders also lived in zip code areas with a higher median per capita income (27.8% lived in an area with a median per capita income of greater than $17 842 per year, compared with 10.7% of responders) and higher educational attainment.

Among participants, individuals with inadequate literacy were older, were more likely to be non-White, and had lower income and education compared with individuals with adequate literacy (Table 1 ▶). They were less likely to have ever smoked cigarettes and less likely to have used alcohol during the past month, and their health status was worse than those with adequate literacy (Table 1 ▶).

A total of 963 (29.5%) participants were hospitalized 1 or more times during follow-up. Individuals with inadequate and marginal functional health literacy were more likely to be hospitalized than were those with adequate literacy (34.9%, 33.9%, and 26.7%, respectively; P < .001 across all 3 groups by χ² test; Figure 1 ▶). Those with inadequate and marginal functional health literacy also were more likely to be hospitalized 2 or more times than were those with adequate literacy (19.9%, 17.8%, and 14.0%, respectively; P < .001; Figure 1 ▶). However, the rate of readmissions among those hospitalized 1 time was similar across the 3 groups (57.0%, 52.4%, and 52.3%, respectively; P = .42).

The time to first hospital admission is shown in Figure 2 ▶. The unadjusted relative risk of hospitalization was 1.44 (95% CI = 1.25, 1.66) for individuals with inadequate functional health literacy compared with those with adequate literacy. Individuals with marginal literacy also were at increased risk (unadjusted RR = 1.29; 95% CI = 1.07, 1.57). The most common discharge diagnoses were congestive heart failure (n = 69), acute myocardial infarction and unstable angina (n = 61), stroke (n = 51), cardiac arrhythmias (n = 46), pneumonia (n = 36), exacerbations of chronic obstructive pulmonary disease or asthma (n = 35), and gastrointestinal hemorrhage (n = 27). The numbers of admissions in any of these categories were too small to determine whether the condition-specific admission rates differed according to functional health literacy, but there were no marked differences in the reasons for admission across groups.

After adjustment for differences in age, sex, race/ethnicity, language, years of school completed, and income, the adjusted relative risk of hospitalization was 1.27 (95% CI = 1.07, 1.52) for individuals with inadequate functional health literacy and 1.22 (95% CI = 1.00, 1.50) for those with marginal literacy, compared with those with adequate literacy (Table 2 ▶). Subsequent models that adjusted for health behaviors, chronic disease prevalence, and self-reported overall health showed almost identical results for people with inadequate literacy (adjusted RR in final model = 1.29; 95% CI = 1.07, 1.55). However, the relative risk for those with marginal literacy declined slightly, to 1.21 (95% CI = 0.97, 1.50) in the final model (Table 2 ▶), which was no longer statistically significant (P = .09). The other significant predictors of hospital admission in the final model were older age, female gender, residence in south Florida, number of chronic diseases, and worse self-reported physical health. Spanish-speaking Hispanic individuals had a lower risk of admission regardless of literacy (adjusted RR = 0.70; 95% CI = 0.52, 0.94). Years of school completed was not significantly associated with the risk of admission.

In addition to the a priori covariates, we conducted an additional model in which the Mini–Mental State Examination score was entered. The Mini–Mental State Examination score was not significant, indicating that the relation between literacy and the risk of hospital admission was not a result of differences in cognitive function. Similarly, social support was not associated with the risk of admission.

The relation between literacy and hospitalization varied substantially according to baseline self-reported physical health, with the effect of literacy being greater for those in better health (P < .001 for the interaction term between inadequate literacy and physical health and P = .05 for the interaction term between marginal literacy and physical health). Thus, the relative risks described above are for individuals whose self-reported physical health was at the mean for the entire study population. Based on models with the interaction terms, the relative risk of hospital admission for individuals whose self-reported physical health was 1 SD above the mean was 1.60 (95% CI = 1.24, 2.07) for those with inadequate literacy and 1.42 (95% CI = 1.02, 1.96) for those with marginal literacy, compared with those with adequate literacy. Conversely, for individuals whose self-reported physical health was 1 SD below the mean, the relative risk of hospital admission was 0.99 (95% CI = 0.83, 1.18) for those with inadequate literacy and 0.99 (95% CI = 0.79, 1.23) for those with marginal literacy, compared with those with adequate literacy. No other interactions were significant.

DISCUSSION

This study provides additional evidence that inadequate health literacy is an independent risk factor for hospital admission. Baker and colleagues9 reported that individuals with inadequate functional health literacy had a 52% higher risk of hospital admission. However, that study was confined to a single public hospital; little information was available on patients’ health behaviors, chronic diseases, and physical functioning; and hospitalizations outside of the study hospital were not captured. In contrast, the current study enrolled community-dwelling elderly individuals in 4 US cities who were cared for by a diverse set of physicians. Detailed information was collected on an extensive set of covariates proven or postulated to affect hospitalization. Administrative claims data were used to determine hospitalizations, which should result in high ascertainment and little potential for systematic bias according to literacy. Thus, this study provides stronger evidence that inadequate functional health literacy is independently associated with the risk of hospital admission.

The relative risk of admission for patients with inadequate literacy was approximately half that reported previously for public hospital patients. The earlier study could have overestimated the association between inadequate literacy and the risk of hospital admission because of incomplete adjustment for confounders. However, the effect of inadequate literacy on hospitalizations may vary, depending on characteristics of the health care system and the patient population. Specifically, the effect of inadequate literacy may be greater for individuals who do not have a regular provider or who face significant administrative barriers to obtaining care, as was the case in the earlier study conducted at a public hospital.

The relation between functional health literacy and the risk of hospitalization varied substantially according to self-reported physical health. Inadequate literacy did not appear to be a risk factor for individuals whose physical health was below average. This finding was not expected and could have been due to chance. However, the finding also may have resulted because people in poor health are more likely to receive assistance in their medical care from family, friends, or home health care workers. For example, in a national sample of the United States, 27.7% of the elderly persons who rated their health as fair or poor received at least 1 formal home health care visit in 1996, compared with 9.3% of those in good to excellent health.20 Family, friends, and home health care workers may act as “surrogate readers” for individuals with inadequate literacy and thus may mitigate the negative effects of inadequate literacy on patients’ understanding of their medications and self-care instructions.2,21 In contrast, individuals who are in average or above-average health may rely more on their own reading abilities to decipher medical instructions, and this may put them at risk for preventable hospitalizations.

We also examined whether the lack of relation between literacy and hospital admissions among individuals in poor health could have resulted from systematic case management programs that ameliorated the adverse effects of low literacy. However, such programs were not instituted within this managed care plan until 1999, the very end of the follow-up period.

The number of years of school completed was not an important predictor of admissions. This should not be surprising. Someone who is 70 years old completed school approximately 50 years earlier. An individual’s ability to deal with the current demands of being a patient is likely to be more dependent on what has happened in the 50 years following completion of school than on educational attainment at the time of graduation. Previous studies have shown that literacy is a more important predictor of health status and health care use than the number of years of school completed,9,22 and this may be particularly true among the elderly. Studies that use years of school completed as a study variable may be unable to detect or may underestimate the relations between patients’ ability to process health care information, health care use, and health outcomes.

This study had several limitations. Most important, only half of the eligible participants completed the study, and nonparticipants appeared to be of slightly higher socioeconomic status. However, hospitalization rates were comparable (29.5% for participants, 27.4% for those who refused to participate, and 27.8% for those whom we were unable to contact). This suggests that the study population was similar to the overall population and that our findings are likely to be representative of the broader group of plan enrollees. Nevertheless, the relation between literacy and hospital admission among study participants may have differed from that among nonparticipants.

We were unable to analyze differences in the reasons for hospital admission. Specifically, we had inadequate power to analyze differences in the risk of preventable hospitalizations or differences between medical admissions and elective surgical admissions. In addition, although we had extensive information on possible confounding variables, this information was based on self-report. If individuals with inadequate functional health literacy were less likely to be aware of chronic medical conditions such as hypertension and diabetes, our adjustments for these variables in multivariate modeling may have been incomplete. We also had a relatively short follow-up period, and the risks of hospital admission for those with inadequate and adequate literacy appeared to be continuing to diverge at the end of the study period. Thus, this analysis could have underestimated the magnitude of the association between literacy and hospitalization. Finally, although we used health literacy as our main independent variable, we cannot state whether the relation between literacy and the risk of hospital admission would have been weaker or stronger if we had used a more general measure of reading comprehension.

Substantial evidence now indicates that inadequate functional health literacy adversely affects patients’ knowledge, self-care for chronic diseases, health status, and risk of hospitalization.23 However, to what degree the negative effects of inadequate literacy can be reduced remains unclear. Previous studies have shown that a patient education brochure for patients with low literacy can improve rates of immunization for pneumococcus,24 and special graphics designed for individuals with low literacy may improve retention of presented information.25 Nevertheless, inadequate literacy is more than just a reading problem. These individuals have global problems with both oral and written communication. Although rewriting health care information at a simpler level would greatly increase the number of people who could understand written health information,26 many patients are unlikely to comprehend even the simplest written materials.

Additional efforts are needed to develop audiovisual aids and other tools to help communicate essential health care information to these patients, and large-scale intervention programs with careful evaluations are needed to determine whether these methods are successful. It may be useful to think of limited health literacy analogously to physical disabilities: we do not expect patients in wheelchairs to climb stairs to reach the hospital. Similarly, health care information should be made accessible to all individuals, regardless of reading ability.