Reliability of the spot urine protein/creatinine ratio for assessing proteinuria in patients with renal disease

Objective: This study aimed to assess the reliability of the spot urine protein/creatinine (sP/Cr) ratio for evaluating proteinuria across different ranges and renal functions. Methods: In this retrospective study, we analyzed 24-hour urine protein excretion (24 h UP) and sP/Cr measurements in 216 patients with renal disease. Pearson correlation and Bland-Altman analyses were performed to evaluate the correlation and agreement between 24 h UP and the sP/Cr. Results: The patients were categorized into the following three 24 h UP groups: 150 to 299 mg/24 hours, 300 to 3499 mg/24 hours, and >3500 mg/24 hours. Significant positive correlations were found between the sP/Cr and the first two 24 h UP groups (r = 0.9104 and r = 0.9721, respectively) but not between the third group (r = 0.3110). Bland-Altman analysis confirmed good agreement in the group with <3500 mg/day proteinuria. Estimated glomerular filtration rates >= 60 mL/minute and <60 mL/minute were significantly correlated with the sP/Cr (r = 0.8714 and r = 0.4516, respectively). Conclusion: The sP/Cr ratio is a reliable indicator for non-nephrotic proteinuria, irrespective of renal function, but is unreliable for nephrotic-range proteinuria.