Comparison of 24-hour urinary protein and protein-to-creatinine ratio in the assessment of proteinuria

To determine the correlation between protein-to-creatinine ratio (PCR) and 24-hour urinary protein (UP), we measured proteinuria in 68 patients attending the nephrology clinic at Jordan University Hospital by 24-hour urine protein excretion and protein-to-creatinine ratio. The cutoff values for spot urine protein-to-creatinine ratio in predicting 24-hour protein threshold excretion of 0.5, 1.0 and 3.5 g/day were determined using receiver operating characteristic curves. A very good correlation (r= 0.832, P 0.0001) was found between spot urine protein-to-creatinine ratio and 24-hour urine protein excretion. Bland-Altman plot showed the two tests had reasonable limits of agreement at low level of protein excretion but the limits became wider as the protein excretion increased. For protein excretion 2.0 g/day, the limits of agreement of spot urine (PCR) and (UP) were +1.48 and -1.2 g/day. The spot urine protein-to-creatinine ratios of 0.72 (sensitivity 0.97; specificity 1.0), 1.2 (0.97; 0.89) and 3.23 (1.0; 0.86) mg/mg reliably predicted 24-hour urine total protein equivalent thresholds of 0.5, 1.0 and 3.5 g/day, respectively. We conclude that the protein-to-creatinine ratio in spot urine specimens is an accurate, convenient, and reliable method to estimate the protein excretion in urine. However, the protein-to-creatinine ratio will likely be within clinically acceptable limits only when proteinuria is at reasonably low levels.