Protein-osmolality ratio for quantification of proteinuria in children

Proteinuria is an important factor for renal injury and prognosis in many diseases. The most valuable method for evaluation of proteinuria is quantitative protein analysis in appropriately 24-h collected urine. But urine collection is difficult and cumbersome especially in children and working adults. The aim of the present study is to define the usefulness of urinary protein/urine osmolality (Uprot/Uosm) ratio in quantification of proteinuria. One hundred and seventy-one patients whose age ranged between 3 and 14 years were included in the study. Uprot/Uosm (r = 0.85, P < 0.001) and urinary protein/creatinine Uprot/Ucrea (r = 0.81 and P < 0.001) ratios were significantly correlated with 24-h protein excretion. Twenty-four-hour protein excretion was correlated with Uprot/Ucrea (r = 0.76, P < 0.001) and Uprot/Uosm (r = 0.79, P < 0.001) ratios in proteinuric group. But, there was no correlation between Uprot/Uosm and Uprot/Ucrea ratios with 24-h protein excretion in non-proteinuric group. The positive and negative predictive value of Uprot/Uosm ratio of 0.28 mg/l/mOsm/kg was 89.9 and 90.8% and Uprot/Ucrea ratio of 0.24 mg/mg was 85.7 and 90% for estimating proteinuria (above 4 mg/m2 h(-1)). The 95th percentile of Uprot/Uosm ratio was 0.25 mg/l/mOsm/kg and Uprot/Ucrea ratio was 0.27 mg/mg in normal group. The best estimate was Uprot/Uosm ratio of 1.42 (sensitivity 100%, specificity 94.9%) and Uprot/Ucrea ratio of 0.75 (sensitivity 100%, specificity 92.9%) for nephrotic proteinuria (40 mg/m2 h(-1)). Uprot/Uosm which is a reliable and simple method can be used for quantification of proteinuria in pediatric patients with normal renal function. Using Uprot/Uosm ratio for quantification of proteinuria can remove the necessity of 24-h urine collection, urine creatinine measurement and spending additional cost and time if the center measures the urine osmolality routinely in urine analysis.