We found higher prevalence of albuminuria among African Americans, Hispanics, Asians, and American Indians/Alaska Natives compared with non-Hispanic whites in the KEEP population, and the differences persisted even after adjustment for demographics, diabetes, hypertension, obesity, and socioeconomic factors. Furthermore, the racial/ethnic differences were not uniform. Risk for prevalent macroalbuminuria was highest for Hispanics and American Indians/Alaska Natives. Among participants without known diabetes or hypertension, only American Indians/Alaska Natives were at higher risk for prevalent albuminuria. While diabetes and hypertension seem to play major roles in higher prevalence of albuminuria among all racial/ethnic groups, further independent risk appears to be present among American Indians/Alaska Natives in isolation of these established risk factors.
Reasons for the higher albuminuria prevalence among American Indians/Alaska Natives are likely multi-factorial and may include genetics, environmental factors, or further residual confounding. The population comprises more than 500 unique tribes that are culturally diverse and geographically dispersed in rural and urban settings.23
Diabetes, an important risk factor for albuminuria, is increasing in this population.18;24;25
Hypertension is also a strong and independent risk factor for albuminuria in this population.18
American Indians/Alaska Natives may have some shared genetic predisposition to albuminuria,26
or the risk may be related to environmental factors that are unaccounted for, or to exposure to toxins such as heavy metals like lead, cadmium, and uranium.27;28
Some of the increased risk observed among American Indians/Alaska Natives without diabetes or hypertension could be related to higher prevalence of earlier stages of these conditions, such as prediabetes and prehypertension, metabolic syndrome, or cardiovascular disease that we were unable to account for in this study.29
Prior studies of albuminuria have focused on diabetic patients, on a specific health maintenance organization group, or on population samples, such as NHANES, with racial/ethnic representation limited to African Americans and Mexican Americans. Our study examined differences in prevalent albuminuria among multiple racial/ethnic groups from throughout the United States and included participants with and without known diabetes and hypertension. Among African Americans, Hispanics, and Asians, we found higher prevalence of albuminuria consistent with prior studies.2;15;16
These results were not surprising, given the strong association of albuminuria with development of ESRD11;12;30;31
and the known differences in ESRD incidence and prevalence among racial/ethnic minorities.2
The risk for macroalbuminuria was also particularly strong among Hispanics, and could be related to their burden of diabetes and hypertension.32
Prevention, early detection, and aggressive treatment of diabetes and hypertension might help reduce racial differences in albuminuria.
The National Kidney Foundation released a position statement on testing for CKD, which can be done with two simple tests: a urine test to detect proteinuria and a blood test for information to estimate GFR.33
According to the National Kidney Disease Education Program, health care professionals should screen persons with diabetes, persons with hypertension at the time it is diagnosed and then every three years, and persons with family history of ESRD at least every three years; most of these recommendations are opinion based.34
Providers should also consider that the risk of kidney failure is higher for African Americans, American Indians/Alaska Natives, and Asians.34
Our findings strongly suggest an indication to consider screening all American Indians and Alaska Natives aged older than 18 years for albuminuria, in addition to those with diabetes as recommended by the Indian Health Service.35
In other groups, screening for albuminuria in people with diabetes or hypertension and family history of CKD may be adequate, particularly among African Americans, Hispanics, and Asians. Screening for albuminuria identifies individuals at increased renal risk.36
Such screening may be cost-effective among people with diabetes and hypertension,37
and it is an important part of a public health approach to CKD.38;39
As this is a cross-sectional study, we cannot determine causality or account for changes in outcomes or risk factors over time. Our cohort is derived from a group of voluntary, screened participants, of which more than 60% were women, in KEEP, a program that targets individuals at elevated risk for kidney disease. Therefore, our results may overestimate prevalence of albuminuria among the racial/ethnic groups represented. However, CKD in the KEEP cohort has been shown to be similar to CKD in the subgroup of participants with CKD in NHANES.40
Some of the data are based on self-report from questionnaires and therefore subject to potential recall and ascertainment bias, but ascertainment of disease status by self-report has been shown to be valid.41
In general, participants with and without missing data in our study were similar, except that those with missing data had a slightly higher prevalence of diabetes and hypertension; thus we may have underestimated the effect of these two conditions in our results. As single measurements of urine albumin and creatinine were used rather than repeated measurements over time as recommended for clinical practice,5
prevalence of albuminuria might be overestimated. However, single urine samples have been accepted as adequate for the detection of albuminuria.42
Lastly, we did not have information regarding treatment with specific medications indicated for albuminuria, such as angiotension-converting enzyme inhibitors, which can cause regression of albuminuria. If these agents were prescribed differently among the racial/ethnic groups, this could potentially be a missed confounder in this study.
Effective screening of specific racial/ethnic groups at increased risk may lead to improved detection of early CKD, allowing early intervention that may help those at highest risk for complications such as cardiovascular disease and progression to ESRD. Future studies are needed to assess the effectiveness of earlier screening for albuminuria in these at-risk populations for prevention of renal outcomes, cardiovascular outcomes, and mortality.