Correlation and consistency analysis of urinary protein-creatinine ratio and 24-h urine protein quantification in patients with chronic kidney disease

Objective To explore the correlation and consistency between morning urinary protein-creatinine ratio(uPCR) and 24 h urine total protein quantification(24 hUTP) in chronic kidney disease(CKD) patients for evaluating the feasibility of replacing 24 hUTP with morning uPCR.Methods Clinical data were retrospectively reviewed for 1793 CKD non-dialysis from January 1, 2019 to December 31, 2021.Spearman's correlation analysis was utilized for examining the correlation and intraclass correlation coefficient(ICC) for evaluating the consistency in different methods of urinary protein detection.Comparisons were also performed for different CKD stages, 24 hUTP and primary diseases.Receiver operating characteristic(ROC) curves of morning uPCR were plotted separately using 24 hUTP 0.15 g, 1.0 g, 3.5 g as three critical points for determining the optimal diagnostic value of morning uPCR for predicting 24 hUTP.Results A positive correlation existed between morning urinary uPCR and 24 hUTP in CKD patients(r=0.880, P<0.001).The correlation was not affected by CKD stage or primary disease, r was between 0.688 and 0.911(both P<0.001) while it was affected by the level of proteinuria.In 24 hUTP ≤ 150 mg and 24 hUTP>3.5 g groups, the associations of morning uPCR with 24 hUTP were weaker, r were 0.300 and 0.380 respectively(both P<0.001).A moderate consistency existed between morning uPCR and 24 hUTP(ICC=0.618, P<0.001).Across different CKD groups and primary diseases, ICC values were between 0.366 and 0.710(P<0.001).However, in comparison between different 24 hUTP groups, the consistencies between uPCR and 24 hUTP were negligible and ICC values were all less than 0.29.ROC analysis showed that, when 24 hUTP was 0.15 g, 1 g, 3.5 g, morning urinary uPCR was 0.335 g/g, 0.975 g/g, 2.38 g/g as its optimal diagnostic value.Conclusion In CKD patients, morning uPCR has an excellent correlation with 24 hUTP.The correlation is not affected by CKD stage or primary disease, but affected by proteinuria level.When 24 hUTP>3.5 g or ≤ 150 mg, the associations are weaker.Morning uPCR amount cannot be simply equated to 24 hUTP amount.Large prospective studies are still required for redefining the correlation threshold of uPCR.