A New Gender-Specific Formula to Estimate 24-Hour Urine Protein from Protein to Creatinine Ratio
Marco Mayayo, M. Paz
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Background: The quantification of proteinuria with the protein to creatinine ratio (PCR) is influenced by the excretion of creatinine, which, in turn, varies according to muscle mass and hence, to gender. Aims: To assess the difference between urine PCR and 24-hour urine proteinuria in men and women and to provide a formula to overcome bias caused by gender. Methods: Four hundred and forty four CKD patients were randomly divided into 2 groups: 70% were used to develop the models, while the remaining 30% were reserved to validate the formula. Epidemiological data were analyzed with chi-square and Student's t tests. Association between 24-hour proteinuria and PCR was studied with Spearman coefficient in men and women separately. Multivariate analysis was used to find variables predictive of disagreement between the 24-hour urine protein and the PCR. Equations to predict 24-hour proteinuria from PCR for men and women were plotted and validated. Results: Disagreement between 24-hour proteinuria and PCR was more pronounced in men (2.16 and 1.64 g in mean, respectively) than in women (2.00 and 2.06 g in mean, respectively). Age and gender were independent predictors of disagreement. Gender-specific equations for predicting 24-hour proteinuria were: males: 24-hour proteinuria = 1.3350*exp0.9108*ln(PCR); females: 24-hour proteinuria = 1.0068*exp0.9030*ln(PCR). Conclusions: Estimation of proteinuria with the PCR improves accuracy if gender-specific equations are used. Use of the PCR without correction for gender leads to the underestimation of proteinuria in men and overestimation in women.