Body mass index is associated with altered renal hemodynamics in non-obese healthy subjects

Background. Weight excess is associated with increased renal risk. Data in overt obesity suggest a role for altered renal hemodynamics. Whether body mass index (BMI) is also relevant to renal function in non- obese subjects is unknown. Methods. We studied the relation between BMI and renal hemodynamics in 102 healthy, non- obese (BMI < 30 kg/ m 2) subjects [59 males, 43 females, mean age 39 (18- 69) years] in a post- hoc analysis of subjects evaluated as prospective kidney donors or as healthy volunteers in renal hemodynamic studies. Results. Mean ( +/- SD) BMI was 24.0 +/- 2.8 kg/ m(2), mean arterial pressure (MAP) 93 +/- 11 mm Hg, glomerular filtration rate (GFR, iothalamate clearance) 111 +/- 19 mL min/1.73m(2), effective renal plasma flow (ERPF, hippuran clearance) 458 +/- 108 mL/min/1.73m(2), FF (GFR/ ERPF) 0.25 +/- 0.04. On univariate analysis, BMI correlated negatively with ERPF/ 1.73m(2) body surface area (BSA) (r = 0.46; P < 0.001), GFR/1.73m(2) BSA (r = -0.24, P = 0.013) and positively with FF (r = 0.45, P < 0.001), and age (r = 0.47, P < 0.001). On multivariate analysis both BMI and age were independent predictors of ERPF/1.73m(2) BSA (negative) and FF (positive, all P < 0.05). Age was the only predictor of GFR/1.73m(2) BSA (negative). Analyzed for renal function indexed for height (h), BMI correlated negatively with ERPF/ h (r = 0.274, P = 0.005), but not with GFR/ h (r = 0.13, P = 0.899). On multivariate analysis both BMI (positive) and age (negative) were independent predictors for GFR/ h (both P < 0.001). Age was the only predictor for ERPF/ h (negative). Predictors for FF (BMI and age, both positive) were by definition unaltered. Conclusion. The impact of BMI on renal function is not limited to overt obesity, as in subjects with BMI < 30 kg/ m(2) a higher BMI is associated with higher FF, that is, a higher GFR relative to ERPF. This suggests an altered afferent/ efferent balance and higher glomerular pressure (i. e., a potentially unfavorable renal hemodynamic profile) that may confer enhanced renal susceptibility when other factors, such as hypertension or diabetes are superimposed.