Review and Special Articles
Socioeconomic Disparities in Chronic Kidney Disease: A Systematic Review and Meta-Analysis

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Context

Evidence on the strength of the association between low SES and chronic kidney disease (CKD; measured by low estimated glomerular filtration rate [eGFR], high albuminuria, low eGFR/high albuminuria, and renal failure) is scattered and sometimes conflicting. Therefore, a systematic review and meta-analysis was performed to summarize the strength of the associations between SES and CKD and identify study-level characteristics related to this association.

Evidence acquisition

Studies published through January 2013 in MEDLINE and Embase were searched. From 35 studies that met the inclusion criteria, association estimates were pooled per CKD measure in the meta-analysis (performed between 2013 and 2014). Meta-regression analysis was used to identify study-level characteristics related to the strength of the SES–CKD association.

Evidence synthesis

Low SES was associated with low eGFR (OR=1.41, 95% CI=1.21, 1.62), high albuminuria (OR=1.52, 95% CI=1.22, 1.82), low eGFR/high albuminuria (OR=1.38, 95% CI=1.03, 1.74), and renal failure (OR=1.55, 95% CI=1.40, 1.71). Differences in SES measures across studies were not related to the strength of associations between low SES and any of the CKD measures (low GFR, p=0.63; high albuminuria, p=0.29; low eGFR/high albuminuria, p=0.54; renal failure, p=0.31). Variations in the strength of associations were related to the level of covariate adjustment for low eGFR (p<0.001) and high albuminuria (p<0.001).

Conclusions

Socioeconomic disparities in CKD were fairly strong, irrespective of how SES was measured. Variations in the strength of the associations were related to the level of covariate adjustment, particularly for low eGFR and high albuminuria.

Introduction

Chronic kidney disease (CKD) is a major public health problem. CKD affects approximately 10% of the adult population worldwide1, 2 and is associated with a number of adverse health outcomes, including progression to end-stage renal disease as well as cardiovascular and all-cause mortality.3, 4 The high burden of CKD and the adverse health outcomes resulting from CKD warrant screening and prevention, and the exploration of factors beyond traditional risk factors (e.g., diabetes and hypertension).5

Diabetes, hypertension, age >60 years, and a family history of CKD are major risk factors for CKD. Healthcare professionals have been recommended to screen patients presenting with these specific high-risk factors.6 Low SES has not yet been identified in clinical guidelines as a high-risk factor warranting screening for CKD, although CKD has been shown to be associated with low SES.7, 8, 9 This may be due to the substantial variation between studies regarding the strength of the associations between SES and CKD (e.g., ranging from twofold to no or very low CKD risk in low SES).9, 10, 11, 12, 13

Variation in the association between SES and CKD across studies might be due to methodologic or real differences. Methodologic differences may concern how SES and CKD are defined, study design, level of adjustment for covariates, and number of SES categories. The “real” association between SES and CKD may also differ by region and by baseline risk of the study populations. For example, in industrialized countries, studies demonstrate an inverse association between low SES and CKD,14, 15, 16 whereas in industrializing countries the association can be positive.17 Furthermore, certain population subgroups (e.g., African Americans) show larger relative SES differences than others (e.g., whites and Asians in the U.S.).10, 18, 19 The variation in associations between SES and CKD has been summarized in some narrative literature reviews,20, 21, 22, 23 but to the knowledge of the authors, a systematic review has not yet been undertaken.

Therefore, the aim of the study was to (1) summarize the strength of the association between SES and CKD (measured by low estimated glomerular filtration rate [eGFR], high albuminuria, low eGFR/high albuminuria, and renal failure) in a systematic review and meta-analysis and (2) identify study-level characteristics related to the strength of the association between SES and CKD.

Section snippets

Methods

A systematic review was conducted between 2013 and 2014 in accordance with prevailing guidelines for systematic reviews and meta-analysis according to Meta-analysis of Observational Studies in Epidemiology.24, 25 Five authors (PV, UB, MMJ, RTG, and SAR) formed the systematic review team. Three authors had expertise in social epidemiology (PV, UB, SAR), three in renal epidemiology (PV, MMJ, RTG), and all in epidemiology and biostatistics.

Study Selection

A total of 1,701 unique studies were identified by title and abstract screening from the initial search results. Fifty-two studies were selected for full text review, after excluding studies that did not assess SES as exposure (n=1,232) and CKD as outcome (n=339); had an inappropriate study design (e.g., reviews, comments, conference abstracts, and letters) (n=34) or study population (e.g., hospital-based study populations) (n=32); and studies without full text including one article that was in

Discussion

The results of this study suggest that compared to those with high SES, people with low SES have a fairly strong association with CKD defined by low eGFR, high albuminuria, low eGFR/high albuminuria, or renal failure. Different definitions of SES were not related to the strength of associations between low SES and any of the CKD measures. Variations in the strength of the associations were only related to the level of covariate adjustment in cases of low GFR and high albuminuria such that the

Acknowledgments

We thank Truus van Ittersum (information specialist) for helping with the systematic literature search. The funding bodies had no role in the design and conduct of the study; in the collection, analyses, and interpretation of the data; or in the preparation, review, or approval of the manuscript.

No financial disclosures were reported by the authors of this paper.

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