Prospective associations of health literacy with clinical outcomes in adults with CKD: findings from the CRIC study

Abstract

Background: Limited health literacy is associated with significant morbidity and mortality in the general population but the relation of health literacy with long-term clinical outcomes among adults with chronic kidney disease (CKD) is less clear.

Methods: Prospective data from the Chronic Renal Insufficiency Cohort (CRIC) Study (n = 3715) were used. Health literacy was assessed with the Short Test of Functional Health Literacy in Adults (dichotomized as limited/adequate). Cox proportional hazards models were used to separately examine the relations of health literacy with CKD progression, cardiovascular event (any of the following: myocardial infarction, congestive heart failure, stroke or peripheral artery disease), and all-cause, cardiovascular and non-cardiovascular mortality. Poisson regression was used to assess the health literacy-hospitalization association. Models were sequentially adjusted: Model 1 adjusted for potential confounders (sociodemographic factors), while Model 2 additionally adjusted for potential mediators (clinical and lifestyle factors) of the associations of interest.

Results: In confounder-adjusted models, participants with limited (vs adequate) health literacy [555 (15%)] had an increased risk of CKD progression [hazard ratio (HR) 1.34; 95% confidence interval (CI) 1.06-1.71], cardiovascular event (HR 1.67; 95% CI 1.39-2.00), hospitalization (rate ratio 1.33; 95% CI 1.26-1.40), and all-cause (HR 1.54; 95% CI 1.27-1.86), cardiovascular (HR 2.39; 95% CI 1.69-3.38) and non-cardiovascular (HR 1.27; 95% CI 1.01-1.60) mortality. Additional adjustments for potential mediators (Model 2) showed similar results except that the relations of health literacy with CKD progression and non-cardiovascular mortality were no longer statistically significant.

Conclusions: In the CRIC Study, adults with limited (vs adequate) health literacy had a higher risk for CKD progression, cardiovascular event, hospitalization and mortality-regardless of adjustment for potential confounders.

Keywords: CVD; chronic kidney disease; health literacy; hospitalization; mortality.

FIGURE 1:

Hypothesized association of health literacy with clinical outcomes, and potential confounders and mediators of this association (simplified direct acyclic graph). Model 1 was adjusted for potential confounders of the association between health literacy and clinical outcomes (also known as total effect). Model 2 additionally adjusted for potential mediators of the association between health literacy and clinical outcomes (also known as residual effect). The clinical outcomes examined in this study were CKD progression, cardiovascular event(s), hospitalizations and mortality. (a) The potential confounders of the association between health literacy and clinical outcomes include sociodemographic factors (i.e. clinical center, sex, race/ethnicity, education and annual household income). (b) The potential effect mediators of the association between health literacy and clinical outcomes include clinical factors/prior disease (i.e. systolic BP, diabetes, urine protein to creatinine ratio, ACEi/ARB medication use, prior contact with a nephrologist, baseline eGFR, hemoglobin A1C, as well as hyperlipidemia, and aspirin and/or statin medication use).

FIGURE 2:

Associations of limited health literacy (vs adequate health literacy) with clinical outcomes: CKD progression, cardiovascular event, hospitalization and mortality, CRIC Study. (a) Model 1 (adjusted for potential confounders, also known as total effect): across all outcomes, Model 1 adjusted for the sociodemographic factors (i.e. clinical center, age, sex, race, education and annual household income). (b) Model 2 (adjusted for potential mediators, also known as residual effect): Model 2 of the CKD progression outcome additionally adjusted for clinical factors (i.e. systolic BP, diabetes, hemoglobin A1C, baseline eGFR, prior contact with a nephrologist, urine protein to creatinine ratio, and use of ACEi/ARB medication) and lifestyle factors (i.e. current smoking and BMI). Model 2 of the cardiovascular event and mortality outcomes additionally adjusted for systolic BP, diabetes, urine protein to creatinine ratio, baseline eGFR, hyperlipidemia, and use of ACEi/ARB, aspirin and/or statin medication. Model 2 of the hospitalization outcome additionally adjusted prior contact with a systolic BP, diabetes, urine protein to creatinine ratio, nephrologist, hemoglobin A1C, hyperlipidemia and use of ACEi/ARB, aspirin and/or statin medication. Cox proportional hazard regression models were used to estimate hazard ratios (HR) for the associations of healthy literacy with failure time outcomes (CKD progression, cardiovascular event and mortality). Poisson regression models were used to estimate rate ratios (RR) for the association between health literacy and hospitalization.