Early signs of nephropathy in adolescents with obesity

Childhood obesity is increasingly recognized as a risk factor for chronic kidney disease; however, early structural and functional kidney alterations remain incompletely characterized.

We conducted a cross-sectional study including 768 adolescents with obesity aged 10-18 years. Kidney function (KF) was assessed using creatinine-/cystatin C-based estimated glomerular filtration rate (eGFR), along with urinary albumin- and protein-to-creatinine ratio (ACR, PCR). Kidney length (KL) and volume (KV) were measured by ultrasound and expressed as standard deviation scores (SDS) using reference values.

Increasing BMI-SDS was associated with lower GFR estimates: creatinine-based eGFR across BMI-SDS categories from 112 to 105 ml/min/1.73 m², cystatin C-based eGFR from 110 to 101 ml/min/1.73 m², and combined creatinine-cystatin C eGFR from 111 to 103 ml/min/1.73 m² (all p < 0.005). Kidney dimensions increased stepwise with adiposity. KL exceeded the 97.5th percentile in 15-19% of participants depending on the reference standards, whereas KV was increased in 48-51% when age-/BSA-based, and 15% when height-based. Albuminuria was uncommon (<5% participants). KV showed significant associations with insulin (r = 0.27), uric acid (r = 0.33), systolic blood pressure (r = 0.33; all p < 0.001). In multivariable linear regression BMI-SDS was independently associated with KV (β = 0.29; 95% CI 0.22-0.36; p < 0.001), inclusion of kidney over-size significantly improved model fit.

Excess adiposity is linked to marked kidney enlargement and BMI-related differences in filtration-marker-derived eGFR estimates. Increased KV is frequent despite low prevalence of albuminuria, supporting KV as a sensitive marker of early obesity-related kidney remodeling. The functional significance of lower estimated eGFR values requires confirmation using measured GFR methods.