[Protein/creatinine ratio in single urine samples for the semiquantitation of proteinuria in children with nephrosis]

OBJECTIVE: To estimate, semiquantitatively, the proteinuria of nephrotic patients by the use of the value of protein/creatinine ratio in single urine samples and determine its correlation with 24-hour proteinuria.METHODS: Analysis of 30 single urine samples and thirty 24-hour urine samples from 20 children with nephrosis followed up at the Division of Pediatric Nephrology of the University Hospital, Faculty of Medicine of Ribeirão Preto, University of São Paulo. Proteinuria in single urine samples and 24-hour urine samples was measured by the turbidimetric method with 3% sulfosalicylic acid. Urinary creatinine concentration was measured by the method of Hare, modified by Haugen and Blegen, adapted to the microtechnique.RESULTS: An excellent correlation was observed between 24-hour proteinuria and the protein/creatinine ratio in single urine samples, by linear regression analysis before (r = 0.82; p < 0.001) and after logarithmic transformation (r = 0.93; p < 0.001). All patients with 24-hour proteinuria at physiological levels (less than 0.1 g/m(2)/day) had a protein/creatinine ratio of less than 0.1 (mg/mg) in single urine samples. All patients with nephrotic 24-hour proteinuria (more than 1.0 g/m(2)/day) had a protein/creatinine ratio of more than 1.0 (mg/mg). The patients with intermediate proteinuria (between 0.1 and 1.0 g/m(2)/day) had a protein/creatinine ratio distributed on the three levels.CONCLUSIONS: The protein/creatinine ratio in a single urine sample is a simple and reliable method for the evaluation of proteinuria and eliminates the errors due to inadequate 24-hour urine collection.