In total, 20,030 subjects responded to the DISTANCE survey and maintained continuous membership at Kaiser. We excluded 3629 individuals with self-reported multiethnic, other, or unknown ethnicity, 306 persons with ESRD, 4984 participants with prevalent albuminuria, and 515 participants with no albuminuria measurement, leaving a total of 10,596 persons in the analytic cohort. Ethnic minorities were well represented, with a relatively balanced proportion of women within each group (). The majority of patients were older, with a mean age of approximately 60 years, and 70% to 95% had diagnosed hypertension or hyperlipidemia. A larger proportion of Hispanics, Filipinos, and blacks had A1C levels of >8% compared with whites and Asians. In contrast, Hispanics, Asians, and Filipinos had better blood pressure control compared with whites and blacks (marked by a systolic blood pressure of <130 mg Hg). At baseline, approximately 15% to 25% of the cohort had moderate impairment of kidney function (eGFR <60 mL/min per 1.73 m2) without albuminuria; the highest prevalence of reduced GFR was observed in whites.
Asians, Filipinos, and whites had higher levels of socioeconomic status than blacks and Hispanics based on annual income levels greater than $65,000, college education, and lower levels of neighborhood deprivation. Limited English proficiency was common in Hispanics, Asians, and Filipinos; the vast majority of Filipinos and a large proportion of Asians and Hispanics were not born in the United States. Poor provider communication was more commonly reported by Filipinos and Hispanics than by whites, blacks, and Asians.
There were 981 confirmed incident albuminuria events over 3 years of observation (27,292 person-years of observation). In all, 11% of blacks, 10% of Filipinos, 9% of Asians and Hispanics, and 8% of whites developed albuminuria. The mean observation time and the number of albuminuria measurements per individual appeared to be comparable across ethnic groups (). Seventy percent of the diagnoses were based on 2 positive confirmatory tests (either albumin to creatinine ratio or 24-hour urinary protein); 22% were based on a combination of a dipstick plus either albumin to creatinine ratio or 24-hour urinary protein; and 8% were based on 2 positive dipstick tests (ie, dipstick only). On average, the second (confirmatory) test occurred 9.2 months (SD 5.6 months) after the first positive test. The age-standardized rate of albuminuria (per 1000 person-years) was highest in blacks (27.8, 95% confidence interval [CI] 18.2–38.3), and the CIs did not overlap with those for the reference group (whites: 13.6, 95% CI 10.5–17.0). The confidence intervals did overlap between those for whites and the remaining race groups: Filipinos (22.0, 95% CI 14.0–31.1), Asians (15.0, 95% CI 7.7–23.4), and Hispanics (13.8, 95% CI 11.6–16.2). In fully adjusted models, we observed a 93% greater risk of albuminuria in Filipinos, a 35% greater risk in Asians, and a 22% greater risk in blacks compared with whites.
Association of Ethnicity With Incident Albuminuria
We also attempted to identify potential mediators of the elevated risk of incident albuminuria associated with ethnicity (). Hazard ratios were only slightly attenuated for blacks, changed minimally in Hispanics, and strengthened in Asians and Filipinos. In the final saturated model that included all 34 factors, the risk of albuminuria associated with Asian and Filipino ethnicity increased relative to the base model, particularly when clinical factors were introduced to the model. In supplemental analyses, incidence rates of albuminuria were similar in survey nonrespondents in DISTANCE, as well as in the larger Kaiser Permanente Northern California Diabetes Registry, suggesting selection bias was not a major concern.
Effect of Adjustment for Potential Mediators on the Association Between Ethnicity and Incident Albuminuria