Evaluation of Urinary Indices for Albuminuria and Proteinuria in Patients with Chronic Kidney Disease

BACKGROUND/AIMS: Either protein-to-creatinine ratio (PCR) or albumin-to-creatinine ratio (ACR) can be adopted for estimation of proteinuria in patients with chronic kidney disease (CKD). Estimated protein excretion rate (ePER) and estimated albumin excretion rate (eAER) may be superior to ACR and PCR. Reports show that urine albumin-to-protein ratio (APR) may be useful in detecting tubular proteinuria, but should be compared with urine protein electrophoresis (PEP). METHODS: Both 24-h urine and spot urine were collected from 77 stable CKD patients for measurement of albumin, protein, and creatinine, and PEP. Based on MDRD and CKD-EPI equations, ePERMDRD, ePERCKD-EPI, eAERMDRD and eAERCKD-EPI were calculated to estimate daily proteinuria and albuminuria. Glomerular CKD was defined by clinical and/or pathological evidence. RESULTS: ACR correlated significantly with PCR. However, microalbuminuria was present in patients without pathologic proteinuria. Twenty-four-hour urine albumin correlated better with eAERMDRD and eAERCKD-EPI than ACR, and 24-h urine protein correlated better with ePERMDRD and ePERCKD-EPI than PCR. APR significantly but not well correlated with the albumin fraction in urine PEP. The albumin fraction obtained from urine PEP was significantly higher in patients with glomerulopathy than those with non-glomerular CKD, whereas there were no differences in APR between groups. In contrast with APR, the albumin fraction in urine PEP was independently associated with glomerular CKD. CONCLUSIONS: Both PCR and ACR are useful in evaluation of proteinuria. In quantifying daily proteinuria and albuminuria, ePER and eAER are superior to PCR and ACR, respectively. Compared with APR, urine PEP is more useful in diagnosing glomerular proteinuria.