Abstract
Rationale & Objective
Chronic kidney disease (CKD) disproportionately affects Black adults and those with lower socioeconomic status in the United States. The aim of this study was to examine the associations between socioeconomic status and CKD, albuminuria/stage 1-2 CKD, and stage 3-5 CKD, and to assess differences between Black and White adults.
Study Design
We used data from the 2017-2020 National Health and Nutrition Examination Survey. CKD was defined as an estimated glomerular filtration rate of <60 mL/min/1.73 m2 based on the race-free CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation (stage 3-5 CKD) and/or a urinary albumin-creatinine ratio of >30 mg/g (albuminuria/stage 1-2 CKD).
Setting & Participants
Respondents to the 2017-2020 National Health and Nutrition Examination Survey with Black or White race.
Exposure
Measures of socioeconomic status (income to poverty ratio, insurance status, education, employment status, and health care access).
Analytical Approach
We examined the relationship between measures of socioeconomic status and CKD, albuminuria/stage 1-2 CKD, and stage 3-5 CKD using survey-weighted Poisson regressions controlling for age, sex, and medical comorbid conditions.
Results
The weighted sample (N = 182,622,525) was 52.2% women and 15.5% Black, with a mean age of 49.1 years. The prevalence of CKD was 15.6% in the overall sample, 20.9% among Black adults, and 14.7% among White adults. Higher income, higher education levels, and having health insurance were associated with a lower prevalence of CKD in the overall sample and among White adults, but not among Black adults. This pattern was consistent for those with albuminuria/stage 1-2 CKD, but not for those with stage 3-5 CKD.
Limitations
This study is limited by its cross-sectional design. In addition, data were based on single measurements and thus may be less precise in estimating the prevalence of chronic disease.
Conclusions
Higher socioeconomic status was inversely associated with albuminuria/stage 1-2 CKD and CKD among White but not Black adults. Future work should investigate the mechanisms by which albuminuria/stage 1-2 CKD remains independent of socioeconomic status among Black adults.
Index Words: Albuminuria, epidemiology, health disparities, kidney failure, socioeconomic status
Plain-Language Summary
Chronic kidney disease (CKD) disproportionately affects Black adults and people with lower socioeconomic status in the United States. We looked at the association between socioeconomic status and CKD in the United States using data from the 2017-2020 National Health and Nutrition Examination Survey. We found that higher socioeconomic status was associated with a lower prevalence of CKD in the overall sample and among White adults, but not among Black adults. When we analyzed this relationship by looking at albuminuria/stage 1-2 CKD (urinary albumin-creatinine ratio > 30 mg/g) and stage 3-5 CKD (estimated glomerular filtration rate < 60 mL/min/1.73 m2) separately, we found that this discordant relationship was mostly limited to albuminuria/stage 1-2 CKD.
Chronic kidney disease (CKD) disproportionately affects Black adults, with the risk of kidney failure being nearly 3 times as high among Black adults as among White adults in the United States.1 Similarly, CKD mortality is over twice as high among Black adults as among White adults.2 Some of the disparities in outcomes are related to known differences in disease burden (eg, hypertension) and a higher prevalence of risk alleles such as APOL1.3 However, socioeconomic status is increasingly recognized for its role in health disparities, despite limited research characterizing its relationship with CKD in White and Black adults in the United States.
Evidence on how socioeconomic status might affect the relationship between race and risk of CKD has been conflicting. Whereas several studies showed that lower socioeconomic status (based on household income) was associated with CKD and albuminuria/stage 1-2 CKD among Black adults,4,5 others have found this relationship to be weak.6 Moreover, prior research on this subject was performed before the development of race-free equations for the calculation of the estimated glomerular filtration rate (eGFR),7,8 which is believed to correct underestimates of CKD and its severity among Black adults observed with the race-based eGFR equations.7, 8, 9
Using data from a nationally representative sample of the US population, we investigated the association between multiple measures of socioeconomic status (ie, household income, health care access, insurance status, employment, and education) and the presence of CKD using race-free equations for eGFR, overall and in Black and White adults individually. We hypothesized that the relationship between socioeconomic status and prevalence of CKD would differ between Black and White adults.
Methods
Data Source
We performed a secondary observational analysis of data gathered from participants of the 2017-2020 prepandemic National Health and Nutrition Examination Survey (NHANES). NHANES is a program of studies on noninstitutionalized adults and children in the United States and uses a complex survey design to obtain a properly representative sample.10 NHANES is conducted by the National Center for Health Statistics, a component of the Centers for Disease Control and Prevention.10 NHANES has a survey component that obtains information on participants’ demographic, socioeconomic, and health care use, as well as an examination component that includes laboratory and physical measurements from participants. The data from this study came from the demographic, laboratory, and questionnaire data sets.10 In this analysis, we included 5,925 participants aged 18 years and older and self-identified as Black or White race (Fig S1), with a weighted sample size of 182,622,525. This work was exempt from formal approval and informed consent owing to the publicly available deidentified nature of the data.
Exposure: Measures of Socioeconomic Status
Our primary exposures were participant socioeconomic status based on the income to poverty ratio (PIR), insurance status (“Are you covered by health insurance or some other kind of health care plan?”), education (“What is the highest grade or level of school you have completed or the highest degree you have received?”), employment (“Which of the following were you doing last week?”), and health care access (“Is there are place that you go when you are sick or need advice about your health?”). PIR (ranging continuously from 0-5.00 with top coding at 5.00) was used in this study as a proxy for household income. In determining whether PIR was high or low for reporting prevalence based on socioeconomic strata, those with a PIR above the sample mean of 3.3 were defined as having high PIR. PIR reported in NHANES was calculated as a multiple of an interviewee’s self-reported family income in dollars as compared with the federal poverty line.11 Insurance status, health care access, and employment were categorized as yes versus no. Education was classified into the following 5 categories: 9th grade, 9th-11th grade, high-school graduate, some college, and college graduate or above.11 In reporting a high or low education level, those with some college or above were defined as having high levels of education.
Outcome: CKD, Albuminuria/Stage 1-2 CKD, and Stage 3-5 CKD
Our primary outcome was CKD. CKD was defined as an eGFR of <60 mL/min/1.73 m2 based on the race-free CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation and/or a urine albumin-creatinine ratio of >30 mg/g.8,12 Race-free versions of the equation for eGFR were published in 2021 and are recommended for use by the National Kidney Foundation and American Society of Nephrology.8,13 Our secondary outcomes were albuminuria/stage 1-2 CKD (defined as an albumin-creatinine ratio of >30 mg/g with an eGFR of ≥60 mL/min/1.73 m2) and stage 3-5 CKD (defined as an eGFR of <60 mL/min/1.73 m2). Biomarkers for CKD were collected as part of the laboratory component of NHANES in which NHANES collected biospecimens for analysis. A phlebotomist collected blood and participants provided urine specimens.14
Other Covariates
We examined the following covariates: sex, age, hypertension, diabetes, and high cholesterol. Sex was categorized as male or female, based on participant self-report. The participant’s age was recorded at an initial screening visit (participants aged 80 years and over were top coded as 80 years old to maintain privacy).15 Hypertension was determined by a systolic blood pressure reading of >130 mm Hg or a diastolic blood pressure reading of >80 mm Hg based on the average of 3 consecutive electronic oscillometric readings.11,16 Diabetes was determined based on participant hemoglobin A1c ≥6.5%.11,17 High cholesterol was determined via participant response to the question “[h]ave you ever been told by a doctor or other health professional that your blood cholesterol level was high?” Obesity was based on a body mass index of ≥30 kg/m2, derived using height and weight measurements conducted during the examination component of NHANES visits.10
Analysis
We conducted all analyses using NHANES-recommended survey weights.18 We used survey-weighted Poisson regressions to calculate risk ratios (RR) for the prevalence of CKD, albuminuria/stage 1-2 CKD, and stage 3-5 CKD based on socioeconomic status measures (ie, PIR, having insurance, education level, employment status, and health care access). For binary variables (ie, insurance, health care access, and employment status), we compared RRs with reference categories, whereas we treated education and PIR as continuous variables.
In our primary model, we adjusted for age, sex, diabetes, hypertension, obesity, and cholesterol. In a supplemental analysis, we adjusted only for age and sex. To assess whether the associations differed by race, we included interaction terms for socioeconomic status and race (Black vs White) in both models. We then repeated these analyses for albuminuria/stage 1-2 CKD and stage 3-5 CKD separately.
We further modeled the association between income and CKD using a multivariable-adjusted restricted cubic spline plot to explore the potential for a nonlinear relationship. In a sensitivity analysis, we examined prevalence of albuminuria/stage 1-2 CKD among Black and White adults stratified based on known CKD risk factors (eg, hypertension and diabetes). In further sensitivity analyses, we set the reference group for both albuminuria/stage 1-2 CKD and stage 3-5 CKD to include only participants without any form of kidney disease (ie, neither albuminuria/stage 1-2 CKD nor stage 3-5 CKD). This was done to ensure that the results were not affected by including people with albuminuria/stage 1-2 CKD in the reference group for stage 3-5 CKD, or people with stage 3-5 CKD in the reference group for albuminuria/stage 1-2 CKD, as was done in the main model.
We performed all analyses using Stata version 14.2 (Stata Corp). We considered a 2-sided P value of <0.05 as statistically significant.
Results
The weighted sample (N = 182,622,525) included 52.2% female participants, with 84.5% self-identifying as White and 15.5% as Black. The mean age was 49.1 years (Table 1 and Fig S1). Compared with White participants, Black participants were less likely to have health insurance (80.8% vs 91.5%) and were less likely to have some college education or above (55.6% vs 66.7%). Black participants had a higher prevalence of CKD (20.9% vs 14.7%) and albuminuria/stage 1-2 CKD (12.7% vs 8.7%) than White participants.
Table 1.
Characteristics of 2017-2020 NHANES Participants in This Analysis
| Characteristics (% or Survey Means [95% CI]) | Overall | Non-Hispanic Black | Non-Hispanic White |
|---|---|---|---|
| Na | 182,622,525 | 28,317,938 | 154,304,587 |
| Age (y) | 49.1 (47.9, 50.4) | 45.4 (44.2, 46.5) | 49.8 (48.5, 51.2) |
| % female | 52.2 (50.0, 54.6) | 55.2 (53.3, 57.1) | 51.7 (49.1, 54.2) |
| % with health insurance | 89.9 (87.0, 92.1) | 80.8 (78.2, 83.2) | 91.5 (88.3, 93.9) |
| % with employment | 63.0 (61.2, 64.7) | 62.2 (58.9, 65.5) | 63.1 (61.0, 65.1) |
| % with some college or greater | 65.0 (61.4, 68.5) | 55.6 (52.4, 58.8) | 66.7 (62.4, 70.8) |
| Mean income to poverty ratiob | 3.3 (3.2, 3.4) | 2.3 (2.2, 2.5) | 3.4 (3.3, 3.6) |
| % with health care access | 85.9 (83.6, 88.0) | 84.4 (81.0, 87.4) | 86.2 (83.9, 88.5) |
| % with CKD | 15.6 (13.9, 17.6) | 20.9 (18.3, 23.8) | 14.7 (12.4, 16.9) |
| % with albuminuria/stage 1-2 CKD | 9.3 (8.0, 10.8) | 12.7 (10.9, 14.7) | 8.7 (6.9, 10.5) |
| % with stage 3-5 CKD | 6.3 (5.3, 7.5) | 8.2 (6.9, 9.8) | 6.0 (4.9, 7.3) |
Abbreviations: CI, confidence interval; CKD, chronic kidney disease; NHANES, National Health and Nutrition Examination Survey.
N represents the weighted sample size. The overall unweighted sample includes 5,925 adults (2,555 non-Hispanic Black and 3,370 non-Hispanic White).
Calculated as a multiple of interviewees’ self-reported household income as compared with the federal poverty line.
In White participants and the overall sample, CKD prevalence was lower among those with a higher PIR and higher education levels, but this pattern was not observed for Black participants (Table 2). Black participants with insurance were more likely to have CKD, whereas prevalence did not vary based on insurance status for White adults. Across all groups, those with employment were less likely to have CKD. By contrast, across all groups, those with health care access were more likely to have CKD. Similarly, among the overall sample and among White participants, albuminuria/stage 1-2 CKD prevalence was lower among those with a higher PIR, insurance, and higher education, but prevalences were similar across these groups for Black adults. Across all groups, people with employment were less likely to have albuminuria/stage 1-2 CKD, whereas people with health care access were more likely to have albuminuria/stage 1-2 CKD. In White adults and in the overall sample, there was a lower prevalence of stage 3-5 CKD in people with a higher PIR, but this was not seen for Black adults. Across all groups, the prevalence of stage 3-5 CKD was higher for those with insurance and health care access but lower for those with employment and higher education.
Table 2.
Survey-Weighted Prevalences of CKD, Albuminuria/Stage 1-2 CKD, and Stage 3-5 CKD Based on Socioeconomic Strata
| Measures of Socioeconomic Status | Overall | Non-Hispanic Black | Non-Hispanic White | |
|---|---|---|---|---|
| CKDa | ||||
| PIRb | High | 13.0 (11.0, 15.0) | 20.6 (17.7, 23.9) | 12.0 (10.0, 14.3) |
| Low | 20.9 (18.0, 24.2) | 21.2 (18.1, 24.7) | 20.8 (17.1, 25.1) | |
| With insurance | Yes | 15.8 (14.0, 17.7) | 22.3 (19.5, 25.4) | 14.7 (12.6, 17.1) |
| No | 14.6 (11.4, 18.4) | 14.9 (12.1, 18.1) | 14.4 (10.5, 19.5) | |
| Education levelc | High | 13.2 (11.3, 15.4) | 19.6 (17.1, 22.2) | 12.2 (10.1, 14.7) |
| Low | 20.6 (18.1, 23.3) | 23.1 (19.1, 27.7) | 20.0 (17.0, 23.2) | |
| With employment | Yes | 10.4 (8.6, 12.5) | 14.8 (12.2, 17.8) | 9.6 (7.5, 12.2) |
| No | 24.5 (21.6, 27.7) | 31.0 (27.6, 34.6) | 23.3 (20.0, 27.1) | |
| With health care access | Yes | 16.6 (14.7, 18.8) | 22.5 (19.9, 25.4) | 15.6 (13.4, 18.0) |
| No | 9.6 (6.8, 13.3) | 12.2 (7.3, 20.0) | 9.0 (5.9, 13.7) | |
| Albuminuria/stage 1-2 CKD | ||||
| PIR | High | 7.9 (6.3, 9.9) | 12.5 (10.6, 14.8) | 7.4 (5.6, 9.6) |
| Low | 12.1 (10.5, 13.9) | 12.9 (10.4, 15.8) | 11.8 (9.6, 14.5) | |
| With insurance | Yes | 9.0 (7.6, 10.5) | 13.0 (11.8, 15.0) | 8.3 (6.7, 10.3) |
| No | 12.3 (9.8, 15.5) | 11.3 (8.7, 14.5) | 12.8 (9.7, 16.8) | |
| Education level | High | 7.8 (6.2, 9.6) | 12.1 (10.3, 14.2) | 7.1 (5.4, 9.2) |
| Low | 12.2 (10.0, 14.8) | 13.5 (10.4, 17.3) | 11.9 (9.3, 15.1) | |
| With employment | Yes | 8.2 (6.7, 10.0) | 11.6 (9.2, 14.5) | 7.6 (5.8, 9.9) |
| No | 11.2 (9.2, 13.6) | 14.5 (13.0, 16.2) | 10.6 (8.3, 13.5) | |
| With health care access | Yes | 9.4 (8.0, 11.1) | 13.1 (11.3, 15.1) | 8.8 (7.1, 10.8) |
| No | 8.7 (6.0, 12.5) | 10.6 (6.0, 18.1) | 8.3 (5.3, 12.8) | |
| Stage 3-5 CKD | ||||
| PIR | High | 5.0 (4.2, 6.1) | 8.1 (6.2, 10.4) | 4.7 (3.8, 5.7) |
| Low | 8.8 (6.9, 11.2) | 8.3 (6.3, 11.0) | 9.0 (6.9, 11.7) | |
| With insurance | Yes | 6.8 (5.7, 8.0) | 9.3 (7.6, 11.4) | 6.4 (5.3, 7.7) |
| No | 2.2 (1.2, 4.2) | 3.6 (2.5, 5.2) | 1.6 (0.5, 5.1) | |
| Education level | High | 5.5 (4.4, 6.8) | 7.5 (6.0, 9.2) | 5.1 (4.0, 6.6) |
| Low | 8.4 (7.2, 9.7) | 9.6 (7.7, 11.9) | 8.1 (6.7, 9.7) | |
| With employment | Yes | 2.2 (1.5, 3.3) | 3.2 (2.5, 4.1) | 2.0 (1.2, 3.3) |
| No | 13.3 (11.5, 15.4) | 16.5 (13.5, 20.0) | 12.7 (10.7, 15.0) | |
| With health care access | Yes | 7.2 (6.1, 8.5) | 9.5 (7.9, 11.3) | 6.8 (5.6, 8.2) |
| No | 0.9 (0.3, 2.8) | 1.5 (0.9, 2.6) | 0.7 (0.1, 4.0) | |
Notes: Rows display survey-weighted prevalences of CKD, albuminuria/stage 1-2 CKD, or stage 3-5 CKD stratified based on high or low (for education and income to poverty ratio) or those with (vs without) employment, health insurance, or health care access. N = 5,115 for PIR, N = 5,917 for insurance, N = 5,917 for education, N = 5,670 for employment, and N = 5,923 for health care.
Abbreviations: CI, confidence interval; CKD, chronic kidney disease; CKD-EPI, Chronic Kidney Disease Epidemiology Collaboration; eGFR, estimated glomerular filtration rate; PIR, income to poverty ratio.
CKD (n = 1,678) was defined as an eGFR of <60 mL/min/1.73 m2 based on the race-free CKD-EPI equation and/or a urine albumin-creatinine ratio of >30 mg/g. Albuminuria/stage 1-2 CKD (n = 1,133) was defined as a urine albumin-creatinine ratio of >30 mg/g and an eGFR of ≥60 mL/min/1.73 m2. Stage 3-5 CKD (n = 545) was defined as an eGFR of <60 mL/min/1.73 m2.
PIR was divided into high and low based on the mean of 3.3 for the overall sample.
Education was measured in 5 levels: less than 9th grade, 9th-11th grade, high-school graduate, some college, and college graduate or above. High education was defined as those with some college or above.
Higher income (RR = 0.86; 95% confidence interval [CI]: 0.81, 0.91), having insurance (RR = 0.69; 95% CI: 0.56, 0.86), and a higher education level (RR = 0.84; 95% CI: 0.77, 0.90) were associated with a lower prevalence of CKD in the overall sample (Table 3). When stratified based on race, higher income, having insurance, and higher education were associated with a lower prevalence of CKD among White adults but not among Black adults, with significant interaction terms for race, indicating a different relationship between these measures of socioeconomic status and CKD among White and Black adults.
Table 3.
Associations (95% Confidence Intervals) of Measures of Socioeconomic Status With CKD, Albuminuria/Stage 1-2 CKD, and Stage 3-5 CKD, Based on Race
| Measures of Socioeconomic Status | Overall | P Value | Non-Hispanic Blacka | P Value | Non-Hispanic Whiteb | P Value | P Interactionc |
|---|---|---|---|---|---|---|---|
| CKDd | |||||||
| PIR | 0.86 (0.81, 0.91) | <0.001 | 0.97 (0.92, 1.03) | 0.34 | 0.85 (0.79, 0.91) | <0.001 | 0.001 |
| With insurance | 0.69 (0.56, 0.86) | 0.001 | 1.04 (0.89, 1.22) | 0.61 | 0.62 (0.48, 0.81) | 0.001 | 0.001 |
| Education levele | 0.84 (0.77, 0.90) | <0.001 | 0.97 (0.91, 1.05) | 0.48 | 0.81 (0.74, 0.88) | <0.001 | 0.001 |
| With employment | 0.79 (0.63, 1.00) | 0.05 | 0.80 (0.68, 0.94) | 0.008 | 0.81 (0.60, 1.08) | 0.14 | 0.74 |
| With health care access | 0.91 (0.64, 1.28) | 0.56 | 1.07 (0.68, 1.68) | 0.75 | 0.86 (0.58, 1.28) | 0.44 | 0.71 |
| Albuminuria/stage 1-2 CKD | |||||||
| PIR | 0.87 (0.82, 0.93) | <0.001 | 0.98 (0.91, 1.06) | 0.57 | 0.85 (0.79, 0.92) | <0.001 | 0.02 |
| With insurance | 0.64 (0.51, 0.80) | <0.001 | 1.05 (0.88, 1.23) | 0.59 | 0.54 (0.40, 0.73) | <0.001 | 0.001 |
| Education level | 0.81 (0.72, 0.91) | 0.001 | 0.96 (0.86, 1.08) | 0.47 | 0.78 (0.68, 0.88) | <0.001 | 0.01 |
| With employment | 0.99 (0.74, 1.32) | 0.95 | 0.99 (0.80, 1.22) | 0.93 | 1.00 (0.70, 1.43) | 1.00 | 0.78 |
| With health care access | 0.80 (0.53, 1.20) | 0.27 | 0.91 (0.51, 1.60) | 0.73 | 0.77 (0.49, 1.22) | 0.26 | 0.80 |
| Stage 3-5 CKD | |||||||
| PIR | 0.88 (0.80, 0.97) | 0.01 | 0.98 (0.87, 1.10) | 0.71 | 0.89 (0.79, 1.01) | 0.07 | 0.09 |
| With insurance | 0.92 (0.54, 1.59) | 0.77 | 0.97 (0.63, 1.49) | 0.88 | 1.11 (0.43, 2.83) | 0.83 | 0.51 |
| Education level | 0.89 (0.82, 0.97) | 0.007 | 1.03 (0.94, 1.13) | 0.51 | 0.88 (0.79, 0.99) | 0.03 | 0.02 |
| With employment | 0.67 (0.47, 0.97) | 0.04 | 0.65 (0.47, 0.89) | 0.01 | 0.73 (0.46, 1.16) | 0.17 | 0.58 |
| With health care access | 2.08 (0.73, 5.92) | 0.16 | 2.12 (1.31, 3.42) | 0.003 | 2.14 (0.51, 8.96) | 0.29 | 0.71 |
Notes: Estimates indicate relative risk of CKD, albuminuria/stage 1-2 CKD, or stage 3-5 CKD per 1-unit increment in education level or PIR or for those with (vs without) employment, health insurance, or health care access. Model controlled for age, sex, diabetes, hypertension, obesity, and cholesterol.
Abbreviations: CKD, chronic kidney disease; CKD-EPI, Chronic Kidney Disease Epidemiology Collaboration; eGFR, estimated glomerular filtration rate; PIR, income to poverty ratio.
The weighted sample size (N) = 28,317,952; unweighted sample size (N) = 2,555.
The weighted sample size (N) = 154,304,602; unweighted sample size (N) = 3,370.
Interaction terms defined as each measure of socioeconomic status × race.
CKD was defined as an eGFR of <60 mL/min/1.73 m2 based on the race-free CKD-EPI equation and/or a urine albumin-creatinine ratio of >30 mg/g. Albuminuria/stage 1-2 CKD was defined as a urine albumin-creatinine ratio of >30 mg/g and an eGFR of ≥60 mL/min/1.73 m2. Stage 3-5 CKD was defined as an eGFR of <60 mL/min/1.73 m2.
Education was measured in 5 levels: less than 9th grade, 9th-11th grade, high-school graduate, some college, and college graduate or above.
We observed similar patterns regarding the associations between socioeconomic status and albuminuria/stage 1-2 CKD (Table 3). Higher income (RR = 0.87; 95% CI: 0.82, 0.93), having insurance (RR = 0.64; 95% CI: 0.51, 0.80), and a higher educational level (RR = 0.81; 95% CI: 0.72, 0.91) were associated with a lower prevalence of albuminuria/stage 1-2 CKD. When stratified based on race, income, insurance, and education were associated with a lower prevalence of albuminuria/stage 1-2 CKD among White adults but not among Black adults; interaction terms for race were significant, indicating that the associations between these measures of socioeconomic status and albuminuria/stage 1-2 CKD differed between White and Black adults (P for interaction = 0.001-0.01).
We did not observe consistent associations between measures of socioeconomic status and stage 3-5 CKD (Table 3). A 1-unit higher PIR was associated with a lower prevalence of stage 3-5 CKD in the overall sample (RR = 0.88; 95% CI: 0.80, 0.97) but not among Black or White adults individually (Table 3). By contrast, a higher education level was associated with a lower prevalence of kidney disease among the overall sample (RR = 0.89; 95% CI: 0.82, 0.97) and among White adults (RR = 0.88; 95% CI: 0.79, 0.99) but not among Black adults (RR = 1.03; 95% CI: 0.94, 1.13) with a significant interaction term for race (P = 0.02). Employment was associated with a lower prevalence of stage 3-5 CKD in the overall model (RR = 0.67; 95% CI: 0.47, 0.97) and among Black adults (RR = 0.65; 95% CI: 0.47, 0.89) but not among White adults (RR = 0.73; 95% CI: 0.46, 1.16), although the interaction term for race was nonsignificant (P = 0.58). Health care access was associated with a higher prevalence of stage 3-5 CKD among Black adults (RR = 2.12; 95% CI: 1.31, 3.42) but not among White adults (RR = 2.14; 95% CI: 0.51, 8.96) or in the overall sample (RR = 2.08; 95% CI: 0.73, 5.92) (P interaction = 0.71).
Results were similar when visualized via restricted cubic spline analyses, which were as follows: a higher PIR was associated with a lower prevalence of CKD and a lower prevalence of albuminuria/stage 1-2 CKD in a dose-response fashion in the overall sample (Figs 1A and 2A) and among White adults but not among Black adults (Figs 1B and 2B). In the overall group, there was an inverse association between income and stage 3-5 CKD among participants with a lower PIR (Fig 2C), but there was not an association among Black or White adults individually (Fig 2D). In a further analysis, Black adults with hypertension or diabetes were more likely to have albuminuria/stage 1-2 CKD than White adults with hypertension or diabetes (RR = 1.39; 95% CI: 1.10, 1.75), but the prevalence was not different among those without either hypertension or diabetes (RR = 0.97; 95% CI: 0.62, 1.53) (Table S1). Changing the reference group for those with albuminuria/stage 1-2 CKD to exclude those with stage 3-5 CKD (as opposed to comparing those with albuminuria/stage 1-2 CKD with people with either stage 3-5 CKD or no kidney disease), or changing the reference group for those with stage 3-5 CKD to exclude those with albuminuria/stage 1-2 CKD (as opposed to comparing those with stage 3-5 CKD with people with albuminuria/stage 1-2 CKD or no kidney disease), did not affect the study results (Table S2). Similarly, adjusting only for age and sex did not affect the study results (Table S3).
Figure 1.
Multivariable model--restricted cubic spline plots for the association between income to poverty ratio and prevalence of chronic kidney disease in the (A) overall sample (both races combined, n = 5,220) and for (B) Black (n = 2,155) and White (n = 3,065) adults separately. Model controlled for age, sex, diabetes, hypertension, obesity, and cholesterol.
Figure 2.
Multivariable model 2--restricted cubic spline plots for the association of income to poverty ratio with (A) prevalence of albuminuria/stage 1-2 CKD among the overall sample (n = 5,220); (B) prevalence of albuminuria/stage 1-2 CKD among Black (n = 2,155) and White (n = 3,065) adults; (C) prevalence of stage 3-5 CKD among the overall sample; and (D) prevalence of stage 3-5 CKD among Black and White adults. Model controlled for age, sex, diabetes, hypertension, obesity, and cholesterol. Abbreviation: CKD, chronic kidney disease.
Discussion
In this study, we investigated the association between socioeconomic status and CKD in a nationally representative sample of Black and White adults using race-free estimates of eGFR. Within this sample, Black adults had a higher prevalence of CKD, albuminuria/stage 1-2 CKD, and stage 3-5 CKD. We found that higher levels of most socioeconomic status measures were associated with a lower prevalence of CKD among the sample as a whole and among White adults but not among Black adults. Interaction terms for these measures were significant, indicating that the association between socioeconomic status and CKD differs by race. However, when separated into albuminuria/stage 1-2 CKD and stage 3-5 CKD, we found that this discordant association was largely limited to albuminuria/stage 1-2 CKD. By contrast, socioeconomic status was not associated with stage 3-5 CKD among Black or White adults separately except for when examining the education level among White adults.
We found that most measures of higher socioeconomic status had an inverse association with CKD among White but not Black adults. Most prior research has shown that lower socioeconomic status (across measures such as Zone Improvement Plan (ZIP) code deprivation index, income, and education) is associated with a higher prevalence of CKD.19, 20, 21, 22 However, prior studies have also shown that socioeconomic status (including income and receipt of Medicaid) alone does not fully explain the excess prevalence of CKD among Black adults as compared with their White counterparts.6,23 In addition, a prior meta-analysis on this topic showed that the relative prevalence of CKD in low--socioeconomic status Black adults (measured via area income, education, occupation, and wealth) as compared with their high--socioeconomic status counterparts was lower than that in White adults, which aligns with our current findings of less socioeconomic stratification in CKD among Black adults.6
It is well established that compared with their White counterparts, Black adults have a higher prevalence of CKD and kidney failure.24,25 In a prior analysis, Evans et al26 showed that socioeconomic status in addition to lifestyle behaviors could explain 64% of the excess risk of CKD among Black adults, whereas 10% of the risk was explained by disparities in health care access. Notably, in the current study, health care access was not associated with a lower prevalence of CKD. However, we speculate that this association is likely attributable to reverse causation, owing to increased health care use among patients with CKD and the cross-sectional nature of NHANES.27 This is further supported by our observation that the association with health care access was more pronounced for those with stage 3-5 CKD. Overall, these nationally representative findings indicate that socioeconomic status is not inversely associated with CKD among Black adults. Prior research has noted that some of the excess prevalence of CKD among Black adults may be driven by high-risk APOL1 variants, which are more common among people of West African descent.3 APOL1 can predispose Black adults to progression to more severe kidney disease, independent of other factors. Whether the association between socioeconomic status and CKD might differ by APOL1 status should be the focus of subsequent research.
We also found that most measures of higher socioeconomic status were associated with a lower prevalence of albuminuria/stage 1-2 CKD among the sample as a whole and among White adults but not among Black adults, with significant interaction terms for race across most socioeconomic measures. Prior research has shown a higher prevalence of albuminuria/stage 1-2 CKD among Black adults, which may contribute to a higher risk of kidney failure among this population.28 Notably, the current study found that higher socioeconomic status was not inversely related to albuminuria/stage 1-2 CKD among Black adults. In addition, within the current sample, there was a higher prevalence of albuminuria/stage 1-2 CKD among Black adults with diabetes or hypertension as compared with their White counterparts, but the prevalence was similar among those without either condition. This finding is surprising, given that prior results have shown that Black participants with APOL1 alleles are at an elevated risk of developing albuminuria/stage 1-2 CKD even when adjusting for kidney disease risk factors.29
Finally, we found that although Black adults had a higher prevalence of stage 3-5 CKD than White adults, most measures of socioeconomic status did not have a significant impact on this association among the sample as a whole or among Black or White adults individually. However, we did find that higher income and higher education were associated with a lower prevalence of stage 3-5 CKD in the overall sample. In addition, higher education was associated with a lower prevalence of stage 3-5 CKD among White adults and among the overall sample but not among Black adults, and there was a significant interaction term for race when examining the impact of education on stage 3-5 CKD. As such, some of these mixed associations may be due to the small sample size of participants with stage 3-5 CKD (545 in the unweighted sample), as well as due to higher health care use among people with advanced kidney disease. Regardless, this finding of an inconsistent relationship is surprising, as other studies have shown that lower individual socioeconomic status is a strong predictor of incident CKD (defined by a low eGFR) as well as rapid progression of CKD.22,30 However, some prior studies have shown a mixed association between more severe kidney disease and socioeconomic status. For example, a prior study using data from the Reasons for Geographic and Racial Differences in Stroke study showed that although individual poverty was associated with a higher risk of kidney failure, county-level poverty was not associated with a higher risk of kidney failure.31 As such, further and better-powered studies are required to further understand this relationship, particularly regarding how race affects the relationship between socioeconomic status and advanced kidney disease.
This study has several limitations. NHANES data are cross-sectional, which limits our ability to understand the temporal relationships between cardiometabolic and socioeconomic variables and CKD in this sample. Regarding the study predictors, health care as a measure of socioeconomic status may be subject to reverse causation owing to increased health care use among patients with CKD. In addition, NHANES does not contain genetic data, which limits insights into the impact of factors such as APOL1 on the observed disparities.3,18 In addition, the number of participants with stage 3-5 CKD was small, which might have limited the power of these associations. Finally, data in the current study were based on single measurements and thus may be less precise in estimating the prevalence of chronic disease.
This study also has several strengths. NHANES is a nationally representative sample and as such incorporates people from diverse geographic and socioeconomic backgrounds, which increases the generalizability of our findings.10 In addition, NHANES uses laboratory measurements to estimate kidney function, which provides a higher degree of rigor in the determination of kidney disease within this sample.14 Furthermore, this study used multiple measures of socioeconomic status, which allowed for more thorough evaluation of the association between a range of socioeconomic status factors and kidney disease. Finally, this study uses the new race-free eGFR equations, which differs from many prior studies and more accurately estimates kidney function independent of race. In particular, use of these equations better approximates racial disparities in CKD, as the race-based eGFR equations underestimated the prevalence and severity of CKD among Black Americans.32
This study has multiple clinical implications. This study reinforces the high prevalence of CKD in the United States, which is significantly underdiagnosed and as such requires further public awareness.33 CKD is also responsible for a rising disease burden in the United States and serves as a risk multiplier for morbidity and mortality from other chronic diseases.34 Recent analyses have shown that with the advent of new therapeutics such as sodium-glucose cotransporter-2 inhibitors, population-wide screening for albuminuria/stage 1-2 CKD is likely a cost-effective intervention.35 Given the elevated prevalence of albuminuria/stage 1-2 CKD in minority populations, such screening could help reduce health inequities.
In this study, using a nationally representative sample of the US population and updated race-free equations to estimate kidney function, we found that higher socioeconomic status was inversely associated with CKD and albuminuria/stage 1-2 CKD among White adults but not among Black adults. These findings indicate that socioeconomic status alone does not fully account for racial disparities in CKD and that further investigations and improved treatments are required to reduce excess morbidity and mortality from CKD among Black adults. In particular, future studies with access to more extensive information on ancestry should comprehensively examine ancestry and race to separate the biologic effects of ancestry and the socially mediated effects of structural racism on outcomes in CKD.
Article Information
Authors’ Full Names and Academic Degrees
Benjamin Grobman, BA, Ruth-Alma Turkson-Ocran, PhD, Mingyu Zhang, PhD, MHS, and Stephen P. Juraschek, MD, PhD
Authors’ Contributions
Research area and study design: BG, SPJ, MZ, RATO; data acquisition: BG; data analysis and interpretation: BG, MZ; supervision: SPJ, MZ, RATO. Each author contributed important intellectual content during article drafting or revision and accepts accountability for the overall work by ensuring that questions pertaining to the accuracy or integrity of any portion of the work are appropriately investigated and resolved.
Support
Dr Juraschek is supported by the National Institutes of Health/National Institute on Minority Health and Health Disparities grant R01MD016068. The funders had no role in study design, collection, analysis, interpretation of data, writing of this report, or decision to submit this report for publication.
Financial Disclosure
The authors declare that they have no relevant financial interests.
Acknowledgements
The authors thank the study participants of the National Health and Nutrition Examination Survey, who enabled this research.
Peer Review
Received December 6, 2024. Evaluated by 1 external peer reviewer, with direct editorial input from the Statistical Editor, an Associate Editor, and the Editor-in-Chief. Accepted in revised form May 8, 2025.
Footnotes
Complete author and article information provided before references.
Figure S1: Participant flow diagram.
Table S1: Prevalence of Albuminuria/Stage 1-2 CKD by Hypertension or Diabetes Status.
Table S2: Association of Socioeconomic Status Measures With Kidney Disease With Reference Group Set to Those Without Either Albuminuria/Stage 1-2 CKD or Stage 3-5 CKD.
Table S3: Association of Socioeconomic Status Measures With Kidney Disease. Model Controlled for Age and Sex.
Supplementary Materials
Figure S1; Tables S1-S3.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Figure S1; Tables S1-S3.