The American Medical Association defines health literacy (HL) as ‘the degree to which individuals have the capacity to obtain, process and understand basic health information needed to make appropriate health decisions’ [1]. Identifying a clear relationship between HL and outcomes is important because it may enable health professionals to mitigate the effects of low health literacy (LHL) by clearer communication and reduction of complex care instructions. At routine office consultations, patients may simultaneously receive a variety of lifestyle and therapeutic instructions and many patients with inadequate literacy have difficulty assimilating all this information.
General and specific HL are associated with certain racial and ethnic backgrounds, older age, less formal education and lower socio-economic status and educational attainment [2].
HL may be particularly important for patients with kidney disease because of the complexity of self-care required to improve cardiovascular, metabolic, haematological and other complications they face. It is estimated that 23% of patients with chronic kidney disease (CKD) and 14–32% of dialysis patients have limited HL [3]. In the dialysis population, LHL is associated with higher rates of hospitalization and mortality [3] and in haemodialysis patients it has been linked to poorer health-related knowledge, more healthcare utilization and worse outcomes [4].
In non-dialysis-dependent CKD, LHL has been associated with lower estimated glomerular filtration rate and poorer cardiovascular risk profiles [5]. A 2016 systematic review [6] suggests that adults with moderate–severe CKD, including those on dialysis, might experience a social gradient in access to specialist cardiovascular and nephrology services. Specific factors including low education level, low income, low rates of home ownership and geographic remoteness were significantly associated with worse cardiovascular and mortality outcomes. Of particular note, the review also demonstrates that even within a predominantly insured population, those who are socially disadvantaged have lower access to healthcare than more advantaged dialysis patients. However, the association between HL and CKD awareness may not be straightforward. Saunders et al. [7] confirmed that in an urban, underserved, hospitalized population, both CKD awareness and HL were low and inadequate, but inadequate HL was not associated with low CKD awareness. In other words, both CKD awareness and HL were low, but a low score on one did not predict a low score on the other. According to a recent study, HL was not associated with self-care behaviour after adjustment for potential confounders [8]. However, higher scores of perceived kidney disease knowledge were associated with higher self-reported participation in general CKD self-care. Interestingly, behaviours related to smoking avoidance and adherence to medication and diabetic care routines were high, with dietary practices and exercise notably lower.
This issue of the NDT publishes a systematic review exploring the interrelationship between HL, LHL and worse outcomes in adult non-dialysed CKD patients and interventions to improve these outcomes [9]. This review aimed at identifying potential targets and strategies by summarizing the (rather weak) evidence on patient- and system-level factors that potentially mediate the relationship between LHL and health outcomes. In addition, the review explored the effectiveness of HL interventions that are customized to CKD patients. After a rather strict elimination process, only 48 studies were included from a total of 551 screened records, the large majority of which (73%) came from the USA. This disproportionate representation of US data undoubtedly introduces a substantial bias because of the major differences in healthcare organization, patient comorbidities and social network organization in the USA compared with most European countries. It is important to note that while the US Medicare system does cover up to 90% of people with ESKD once they start dialysis, it does not cover CKD Stages 3–5 and the pre-dialysis population that are <65 years of age. Overall, the majority of HL-tailored intervention strategies that were analysed in the several studies included in the systematic review were unable to detect major long-term behaviour changes that could improve health outcomes in CKD patients. It is somewhat ironic that the majority of these intervention strategies were using online or digital platforms aimed at a population with an overall low general literacy and with limited computer literacy or even without access to this technology. Only strong evidence for an association of LHL with smoking and a suboptimal transplant process was found, with only weak evidence for a variety of other, mostly lifestyle factors that potentially mediate the relation between LHL and health outcomes.
Boonstra et al. [9] found an association of LHL with smoking, a factor well known to be associated with a 50% increased risk for progressive CKD and increased cardiovascular risk. Although smoking prevalence has declined in recent years, distinct populations such as those with LHL, low income and racial/ethnic minorities have disproportionately high smoking rates. Smokers with LHL are also less likely to successfully quit smoking because they have limited access to effective smoking cessation resources or are less likely to use them.
Besides smoking, LHL was also associated with a lower likelihood of being wait-listed for or referred to transplantation. A meta-analysis confirmed that disadvantaged populations with CKD have poorer access to quality treatment, including kidney transplantation [6]. Social determinants such as health insurance status, employment status and education level have been shown to be associated with the incidence of ESKD, access to transplantation and kidney graft survival. On the other hand, French patients living in deprived or advantaged neighbourhoods had the same chance to be placed on the waiting list and to undergo kidney transplantation. They also showed the same mortality risk, after adjustment for their clinical features [10]. This study illustrates the difficulty of making definitive conclusions on the overall role of LHL and its interaction with educational and socio-economic determinants.
Figure 1 illustrates the impact of low HL on renal care.
Impact of LHL on renal care.
A number of essential elements in the systematic review remained undiscussed, likely because of a lack of data: the role of HL in children and, from there, bottom-up to older age strata; the role of ethnicity, faith, public status (migrants, refugees, illegals) and how to reach out to such specific populations; HL and access to home dialysis; HL versus awareness of CKD; the role of lifestyle elements other than smoking (e.g. unhealthy diet, alcohol, sedentarism) and the potential for confounding of HL studies by environmental pollution.
In conclusion, although the systematic review by Boonstra et al. [9] might appear to some extent to be confirmatory in nature, it highlights a number of important facts. First, there is a lack of well-controlled studies in Europe on the impact of HL on the outcome of care in non-dialysed CKD patients, as well as studies on the impact of the diverse European healthcare systems on the level of HL in CKD as compared with other regions. Second, the increasing global interest in patient-centred healthcare implies a shift in thinking about empowering patients to take an active role in their care plan. One of the principal elements in developing a comprehensive patient-centred care plan is using a language that facilitates effective communication between the caregiver and patient. Besides the willingness and the skills of the caregiver, the efficacy of the communication depends also to a large extent on the HL of the patient. There is an obvious need to include this aspect in the medical curricula and the bedside teaching of skills of medical students and nephrology fellows.
The great merit of the systematic review is its drawing attention to the great relevance of adequate HL in CKD patients, a topic that deserves more interest among nephrologists, renal educators, policymakers and other stakeholders.
CONFLICT OF INTEREST STATEMENT
None declared.
(See related article by Boonstra et al. How to tackle health literacy problems in chronic kidney disease patients? A systematic review to identify promising intervention targets and strategies. Nephrol Dial Transplant 2021; 36: 1207–1221)
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