A study on the relationship between urinary protein-creatinine ratio and 24-hour urinary protein quantity in patients with chronic kidney disease

Objective To explore the correlation between urinary protein-creatine ratio (PCR) and 24-hour urinary total protein quantity (24 hUTP) in morning urine and random urine and its predictive equation. Methods A total of 211 patients with chronic kidney disease (CKD) visited to treat in Wuhan First Hospital were selected. The difference and correlation between PCR and 24 hUTP in morning urine and random urine were analyzed. ROC curve was used to analyze the PCR in morning urine and random urine to predict the optimal critical point of 24 h UTP. The equation for predicting 24 hUTP by PCR in morning urine and random urine was established by multiple linear regression method. Results There was no significant difference between PCR and 24 hUTP in morning urine and random urine (P=0.81), but there was a significant positive correlation between morning urine and random urine PCR and 24 hUTP (r=0.90, P<0.01), and there was also a significant positive correlation between PCR and 24 h UTP in random urine (r=0.95, mean P<0.01), which was higher than that in morning urine. The patients were divided into gender, age, 24 h urine volume, etiology, eGFR, Alb, and total cholesterol level groups. A significant positive correlation between PCR and 24 h UTP in morning urine and random urine existed in various groups, with the higher correlation between PCR and 24 h UTP in random urine than that in morning urine. ROC curve analysis showed that, with 0.5 g/24 h, 1.0 g/24 h and 3.5 g/24 h used as the critical point of 24 h UTP, the optimal critical point values of 24 h UTP predicted with PCR in morning urine were 0.70 g/g (sensitivity 84.4%, specificity 86.0%), 1.09 g/g (sensitivity 95.8%, specificity 91.3%) and 3.81 g/g (sensitivity 66.7%, specificity 89.9%), respectively; those predicted with PCR in random urine, 0.56 g/g (sensitivity 93.5%, specificity 75.4%). 1.11g/g (sensitivity 98.3%, specificity 92.4) and 3.43 g/g (sensitivity 87.9%, specificity 89.9%), respectively. The prediction equations of 24 h UTP obtained from PCR in morning urine and random urine were as follows:1 24 hUTP (g)=0.793+0.793×PCR in morning urine+0.124×total cholesterol-0.177×serum albumin (determination coefficient R2=0.87); 224 hUTP (g)=0.369+0.856×PCR in random urine+0.132×total cholesterol-0.092×serum albumin (determination coefficient R²=0.92). The prediction equation for random urine was more accurate that for morning urine. Conclusions There is a good correlation between PCR and 24 hUTP in morning urine and random urine. The correlation is not affected by gender, age, 24 h urine volume, etiology, glomerular filtration rate, serum albumin and total cholesterol level. The correlation for random urine is higher than that for morning urine. The prediction equations can be used to evaluate the prognosis and diagnosis and treatment in patients with chronic renal disease. It is recommended that the prediction equation with PCR in random urine be an alternative method for detection of 24 h UTP.