Renal and Hemodynamic Findings in Children with Obesity: Associations with Central Adiposity, Blood Pressure, and Urinary Markers

Background/Objectives: Data on the earliest renal correlates of childhood obesity are limited. We compared renal, hemodynamic and urinary findings between children with and without obesity and examined their associations with general (BMI) and central (waist-to-hip ratio, WHR) adiposity. Methods: In this prospective cross-sectional comparative study, 43 children with obesity aged 6–18 years and 43 age- and sex-comparable normal-weight controls underwent office blood pressure, serum creatinine, cystatin C and eGFR, 24 h urinary protein, albumin, sodium, NAG and TGF-β1, and ultrasonographic kidney volume (absolute, body-size-indexed and reference-based SDS) measurement. Correlations were examined in the whole cohort and within groups; multivariable models included BMI, WHR, age and sex. Results: Children with obesity had higher office blood pressure (systolic ≥95th percentile in 44.2% vs. 0%) and higher urinary protein, albumin and sodium excretion (all p < 0.001; the sodium difference was no longer significant after indexing to body weight, p = 0.084), with no significant difference in creatinine, cystatin C, eGFR, NAG or TGF-β1; albuminuria >30 mg/day was rare (1 vs. 3). Absolute and BSA-indexed kidney volumes did not differ, height-based SDS was higher in the obesity group, and BMI–kidney volume associations depended on the body-size adjustment used. BMI correlated with blood pressure within both groups and was associated with blood pressure, urinary albumin and sodium after adjustment for WHR, age and sex; the albumin and sodium associations attenuated after additional adjustment for systolic blood pressure. In pooled models WHR was associated with blood pressure (ΔR2 0.02–0.05) but not with urinary markers; this was not demonstrated within the obesity group. Conclusions: Children with obesity showed elevated office blood pressure and modestly higher urinary protein, albumin and absolute—but not weight-indexed—sodium excretion without a difference in eGFR. These exploratory, cross-sectional findings are consistent with, but do not establish, early obesity-associated renal changes and warrant longitudinal confirmation.