Definition of hyperfiltration taking into account age-related decline in renal function in kidney donor candidates with obesity and glucose tolerance disorder.

The definition of hyperfiltration, the main pathogenesis in renal impairment in obesity and diabetes mellitus, is uncertain. Glomerular filtration rate (GFR) declines physiologically with aging, and there is inaccuracy in GFR in obesity due to body surface area (BSA) correction. Here, we defined hyperfiltration using GFR without BSA correction, but with inclusion of aging, and investigated hyperfiltration using this definition and absolute GFR > 125 mL/min. The subjects were 180 kidney donor candidates (56.4 ± 11.3 years old, 79 males). GFR was evaluated using inulin clearance. A two-hour 75-g oral glucose tolerance test was also performed. The subjects were divided into four groups with and without a combination of glucose tolerance disorder and BMI. Normal glucose tolerance (NGT) and BMI < 25 kg/m² were defined as normal, and hyperfiltration was defined as the upper 95% confidence interval of the relationship of aging and GFR in normal cases, and compared with GFR > 125 mL/min. RESULTS: GFR without BSA correction and UAE in non-NGT subjects with obesity were higher than in other groups, but GFR with BSA correction did not show this relationship. In multiple regression analysis, BMI was independently associated with GFR without BSA correction, but not with BSA correction. Aging was consistently associated with GFR. The prevalence of hyperfiltration by our definition (GFR = -0.883 × Age + 167.398) was significantly higher than that using GFR > 125 mL/min (P < 0.0001). Hyperfiltration in obesity and/or glucose tolerance disorder should be evaluated using GFR without BSA correction and including the decline of GFR due to aging.