Correlation between the protein/creatinine ratio in spot urine and 24-hour urine protein.

Abstract

Measurement of the protein content in a 24-hour urine sample is the definitive method of establishing the presence of abnormal proteinuria. However, the urine collection is cumbersome. The spot urine protein to creatinine ratio seems to be a reliable diagnostic tool for urine protein measurement. Our aim was to evaluate the spot urine protein/creatinine ratio against 24-h urine total protein excretion in different proteinuria ranges by comparing samples collected simultaneously in patients of Hospital del Mar during the last year. Observational, cross-sectional study of 159 consecutive paired determinations of 24-h urine total protein excretion and the spot urine protein/creatinine ratio (P/C) in renal patients. The strength of the correlation was determined by calculating the intraclass correlation coefficient (ICC) and the Spearman correlation coefficient (SCC). Among all groups, there was a significant correlation between 24-hour proteinuria and the P/C ratio (SCC: r=0.91, P<0.001). The correlation in different levels of proteinuria were: <300 mg (SCC: r=0.498, P<0.001; ICC: 0.46), 300-3,499 mg (SCC: r=0.828, P<0.001; ICC: 0.66) and ≥3,500 mg (SCC: r=0.181, P=NS; ICC: 0.18). In summary, a strong correlation was observed between spot urine protein/creatinine ratio and 24-h urine total protein excretion in proteinuria levels from 300 mg/day to 3,499 mg/day. A lower correlation was also maintained in 24-h urine total protein <300 mg. In our experience, there is no relevant correlation between spot urine protein/creatinine ratio and 24-h urine total protein excretion in nephrotic-range proteinuria.