Socioeconomic measures and CKD in the United States and The Netherlands

Abstract

Background and objectives: According to the cost of health care utilization systems, there may be regional differences in the relative strength of association of income and education-based socioeconomic status measures with CKD. This study investigated the relative strength of the association of income and education with CKD in a United States and a Dutch population.

Design, setting, participants, & measurements: This cross-sectional study examined individuals who participated in the 1999-2002 National Health and Nutritional Examination Survey (NHANES) and in Prevention of Renal and Vascular End-stage Disease (PREVEND 1997-1998), general population-based cohorts in the United States and The Netherlands, respectively. The main outcome was CKD, defined as estimated GFR <60 ml/min per 1.73 m(2) (using creatinine) or albuminuria ≥ 30 mg/24 hours or albumin-to-creatinine ratio ≥ 30 mg/g.

Results: In NHANES (n=6428), income was strongly associated with CKD (adjusted odds ratio, 2.34 [95% confidence interval (CI), 1.68 to 3.27]; P for trend<0.001) but education was not (adjusted odds ratio, 1.62 [95% CI, 0.87 to 2.25]; P for trend=0.05]. In contrast, in PREVEND (n=7983), low income was weakly associated with CKD whereas low education had a strong association. The fit of the logistic regression model estimating association of income and education with CKD was significantly improved only after income was added in NHANES (P<0.001) and education was added in PREVEND (P=0.01). Sensitivity analyses that used other CKD-defining variables and restricted analyses to participants <65 years of age resulted in similar findings.

Conclusion: In the United States, where access to health care is traditionally income dependent, income appeared more strongly associated with CKD than in The Netherlands, where education showed a stronger association.

Figures

Figure 1.

Association of income quintiles and education levels with CKD in the National Health and Nutrition Examination Survey (NHANES) (left panel) and in Prevention of Renal and Vascular End-stage Disease study (right panel). Presented are odds ratios (95% confidence intervals) for income quintiles (circles and lines) and education levels (squares and lines) adjusted for age, sex, race, and education (for income) or income (for education). Reference categories (category 1) were highest income quintile and highest education level, respectively.