NDT Advance Access originally published online on February 15, 2008
Nephrology Dialysis Transplantation 2008 23(7):2242-2246; doi:10.1093/ndt/gfm949
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Diagnostic accuracy of the protein/creatinine ratio in urine samples to estimate 24-h proteinuria in patients with primary glomerulopathies: a longitudinal study
Post Graduate Program in Medical Sciences: Nephrology, School of Medicine, Universidade Federal do Rio Grande do Sul and Division of Nephrology, Hospital de Clínicas de Porto Alegre (HCPA), Porto Alegre, RS, Brazil
Correspondence and offprint requests to: José Vanildo Morales, Division of Nephrology, Hospital de Clínicas de Porto Alegre, Rua Ramiro Barcelos, n° 2350, sala 2030, CEP 90035-003, Porto Alegre, RS, Brazil. Tel: +55-51-2101-8295; Fax: +55-51-2101-8121; E-mail: jmorales{at}hcpa.ufrgs.br
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Abstract |
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Background. The protein/creatinine (P/C) ratio in urine samples has been used in the clinical management of patients with glomerular diseases. The aim of this study is to perform a prospective evaluation of the P/C ratio accuracy in determining critical levels of proteinuria in patients with glomerulopathies.
Methods. This is a longitudinal study of 41 adult patients with primary glomerulopathies treated with immunosuppressive drugs or angiotensin-converting enzyme inhibitors in a 6-month follow-up. Correlation and agreement level between P24 and the P/C ratio were evaluated. Kappa statistic was employed to evaluate concordance between the two methods taking into account clinically relevant categories of proteinuria. ANOVA for repeated measures was employed. Diagnostic accuracy of the P/C ratio was evaluated by receiver–operator curves (ROC).
Results. There was a significant correlation between P24 and the P/C ratio during the 6-month period (P < 0.001 in all time points). Mean differences between P24 and P/C ratios at baseline and from the first to the sixth month were 2.00, 1.88, 1.22, 1.07, 0.65, 0.34 and 0.57 respectively. In spite of the lower agreement between P24 and the P/C ratio for higher levels of proteinuria, we found substantial Kappa values for categories of proteinuria in all periods. ROC considering the cut-off levels of 0.20 g and 3.5 g for P24 showed that the P/C ratio had a very good accuracy, with areas under the curve of 0.99 (95% CI: 0.97–1.00) and 0.99 (95% CI: 0.99–1.00), respectively.
Conclusion. This longitudinal analysis corroborates the findings of previous cross-sectional studies, supporting the use of the P/C ratio as an accurate test to define critical levels of proteinuria.
Keywords: 24-h proteinuria; nephrotic proteinuria; primary glomerulopathies; protein/creatinine ratio
Received for publication: 3. 3.07
Accepted in revised form: 21.12.07