Comparing Age- and Sex-Specific Reference Values of eGFR between the United States and Europe

The extent to which eGFR varies across populations, in the absence of risk factors and comorbidities associated with kidney disease, remains uncertain. We aimed to develop eGFR reference values in healthy American adults and to compare them with previously described European eGFR reference values. This cross-sectional study compared newly described age-specific and sex-specific creatinine-based eGFR reference values from over 9000 healthy Americans from National Health and Nutrition Examination Survey with previously described eGFR reference values from over 1.5 million healthy individuals in the European CKD Burden Consortium. Health status was based on 14 criteria related to comorbidities, lifestyle factors, and medication use. eGFR was calculated using the European Kidney Function Consortium equation and modeled over the age span and by sex using a generalized additive model. The median eGFR in both 20-year-old American and European men was 98 ml/min per 1.73 m 2 . In both 20-year-old American and European women, the median eGFR was 101 ml/min per 1.73 m 2 . eGFR started to decrease at age 40 years, a result of the structure of the European Kidney Function Consortium equation. By age 79 years, the median eGFR in American and European men was 68 and 67 ml/min per 1.73 m 2 , respectively. The median eGFR in 79-year-old American and European women was 63 and 64 ml/min per 1.73 m 2 , respectively. When removing the effect of comorbidities, lifestyle factors and medication use associated with kidney function, achieved by restricting the analyses to individuals who did not have a presence or history of certain criteria, the distribution of eGFR was similar between healthy Americans and Europeans. This supports the notion that eGFR reference values may be generalizable to populations they were not derived from.