A bedside equation to estimate 24‑h proteinuria in children with nephrotic syndrome: Derivation and temporal validation

To date, 24‑h urine protein (24hUP) excretion remains the gold standard for quantifying proteinuria and is a strong predictor of renal outcomes in glomerular diseases. Although current guidelines allow nephrotic‑range proteinuria to be diagnosed using either single‑void urine protein‑creatinine ratio (UPCR) or 24hUP thresholds, these cut‑offs primarily confirm disease presence and provide limited quantitative guidance for clinical decision‑making during the acute phase of pediatric primary nephrotic syndrome (PNS). The present study thus aimed to provide a method with which to estimate 24hUP in children with PNS. A total of 251 children with PNS were included and divided into a derivation cohort (n=171) and an independent validation cohort (n=80). Log‑log linear regression models were constructed using UPCR adjusted by estimated 24‑h creatinine excretion derived from the Cockcroft‑Gault, Hellerstein and Ghazali‑Barratt equations, with age and sex incorporated as covariates. Model performance was assessed using coefficients of determination (R²), root mean square error (RMSE), mean absolute error (MAE) and calibration analyses. The optimal model, based on Cockcroft‑Gault‑adjusted UPCR, demonstrated good predictive performance in external validation (RMSE, 11.39 mg/m²/h; MAE, 9.26 mg/m²/h; R², 0.91), with 93.8 and 96.3% of estimates within 20 and 30% of observed 24hUP values, respectively. The application of the model indicated that a substantial proportion of children could safely avoid immediate 24‑h urine collection without missing cases of marked proteinuria. On the whole, a bedside equation using adjusted UPCR may serve as a practical surrogate for estimating 24hUP in children with PNS and facilitate clinical decision‑making in routine practice.