Cost-benefit analysis and prediction of 24-hour proteinuria from the spot urine protein-creatinine ratio

Aim: A prospective cross-sectional study was performed on 170 patients with various glomerular diseases to study the accuracy of predicting 24-hour pr oteinuria from the spot urine protein-creatinine ratio (Up/Uc). A cost-bene fit analysis was performed for the New Zealand health economic system to ob tain the best cut-off values for proteinuria. Subjects, methods and results : Two spot urine samples (Up/Ucl and Up/Uc2) were collected on the same day as the collection of a 24-hour urine. A randomly chosen subsample of 50 pa tients provided a second set of urine samples. The correlation and precisio n of agreement between the two methods were examined. The predictive interv als were calculated for derived 24-hour proteinuria. The level of agreement was evaluated by the Bland-Altman method and concordance analysis. The lim its of agreement were evaluated against the clinical Limits of agreement. A cost-benefit analysis (CBA) was performed to obtain the optimum operating points on receiver operating characteristic (ROC) curves for the best decis ion threshold. Correlations of r = 0.97 and 0.99 were observed between Up/U cl, Up/Uc2 and 24-hour proteinuria, respectively. The 95% predictive interv als were wide. A high concordance correlation coefficient was obtained. The most of the differences between the two methods fell within the clinical l imits of agreement. The Up/Ucl of 0.26 and 3.20 represent the best threshol ds to detect normal and nephrotic proteinuria, respectively. Conclusions: D espite wide confidence intervals, a good correlation and precision of agree ment were demonstrated between the two methods across the whole range of pr oteinuria, regardless of the level of renal function. The difference betwee n the two methods was less than the biological variability in the protein e xcretion and its measurement, enabling the methods to be used interchangeab ly. The optimum thresholds for abnormal and nephrotic range proteinuria wer e obtained.