Effects of Race and Sex on Measured GFR: The Multi-Ethnic Study of Atherosclerosis.

Background: Kidney failure disproportionately affects older blacks versus whites. The reasons are unknown and may be related to lower measured glomerular filtration rate (GFR) and higher levels of albuminuria in community-based population samples.

Study Design: Cross-sectional analysis of a substudy of a prospective cohort.

Setting & Participants: Ancillary study following Multi-Ethnic Study of Atherosclerosis (MESA) visit 5.

Predictor: Age, sex, and race.

Outcomes & Measurements: Measured GFR using plasma clearance of iohexol and urine albumin-creatinine ratio (ACR).

Results: GFR was measured in 294 participants. Mean age was 71±9 (SD) years, 47% were black, 48% were women, mean GFR was 73±19mL/min/1.73m, and median ACR was 10.0 (IQR, 5.8-20.9) mg/g. Measured GFR was on average 1.02 (95% CI, 0.79-1.24) mL/min/1.73m lower per year older. Mean GFR indexed for body surface area was not different between blacks versus whites (mean difference, 2.94 [95% CI, -1.37 to 7.26] mL/min/1.73m), but was lower in women than men (mean difference, -9.34 [95% CI, -13.53 to -5.15] mL/min/1.73m); this difference persisted and remained significant after adjustment for demographics, clinical characteristics, and measures of body size. The difference between men and women, but not between blacks and whites, was substantially greater when GFR was not indexed for body surface area. ACR was higher in older versus younger participants (mean difference, 3.2% [95% CI, 1.5%-4.8%] per year), but geometric mean ratio of ACR did not differ between blacks versus whites (mean difference, 19.7%; 95% CI, -39.1% to 6.1%) or between men versus women (mean difference, -4.4%; 95% CI, -27.7% to 26.3%).

Limitations: This is a study of survivors. People who agreed to participate were younger than those who refused.

Conclusions: In this first community-based study that included blacks and whites, no differences in measured GFR between races were found, suggesting that other factors must account for the disproportionately higher burden of kidney failure in older blacks versus whites.