Quantification of proteinuria with urinary protein to osmolality ratios in children with and without renal insufficiency

BACKGROUND: Spot urine is recommended as an accurate method to determine proteinuria in children and adults. However, urinary excretion of creatinine may vary in newborns and spot urine may be influenced by the hydration-dehydration condition of patients. The study was done to assess the validity of the urine protein to osmolality ratio versus the urine protein to creatinine ratio in health and disease conditions. METHODS: We studied the correlation of the urine protein-osmolality ratio (Uprot/Uosm) and the urine protein to creatinine ratio (Up/Ucr) and compared results with the 24-hour urinary protein excretion. Three groups were compared: children with normal renal function and without proteinuria (group 1, n=53), children with normal renal function and with proteinuria (group 2, n=52) and patients with renal insufficiency (group 3, n=45). Early morning urine samples and 24-hour urine specimens were collected for protein, creatinine, and osmolality. RESULTS: The optimal cutoff value of the Uprot/Uosm ratio was determined to be 0.33 mg/L/mosm/kgH2O for abnormal proteinuria and 1.75 mg/L/mosm/kgH2O for nephrotic range proteinuria. In comparing ROC curves, we found no differences between the Uprot/Uosm and Up/Ucr ratios in detecting abnormal proteinuria or nephrotic syndrome in children with normal or decreased renal function (P>0.05). CONCLUSION: Both the Uprot/Uosm and Up/Ucr ratios from random urine specimens are good predictors of 24-hour urinary total protein excretion in children with and without renal insufficiency.