TDK conference 2018

Proteinuria occurs when different types of proteins (e.g. albumin) appear in the urine. Persistent proteinuria is abnormal and is usually a sign of protein losing nephropathy. The renal loss of proteins is mainly caused by either tubular or glomerular dysfunction, and the differentiation between the two types holds a high diagnostic and therapeutic significance. Tubular proteinuria is defined by the loss of low molecular weight proteins, and comparatively small amounts of albumin.

We hypothesized that by assessing the urine albumin-to-total protein ratio (uAPR) we would be able to identify the source of proteinuria (i.e. whether it is solely tubular origin or caused by glomerular damage as well).

The urinary albumin-to-creatinine ratio (UAC), urinary protein-to-creatinine ratio (UPC), and the ratio of UAC and UPC (uAPR) were determined in 28 canine urine samples. The findings were compared to sodium dodecyl sulfate – polyacrylamide gel electrophoresis (SDS-PAGE), which was considered the gold-standard for the determination of the source of proteinuria in this study. The urine specimens were obtained from laboratory beagles and from treated and untreated clinical patients. Subanalyses were performed in the different cohorts.

The median, lower and upper quartile of the UPC was 1.27 (0.48; 3.53), the UAC was 0.51 (0.10; 2.69), and the uAPR was 0.56 (0.15; 0.77) in the urine specimens. With receiver operating characteristic (ROC) curve analysis the ideal cut-off value was determined to be 0.37, below which the tubular proteinuria could be identified with high confidence (sensitivity = 93.75%, specificity = 75.0%, positive predictive value = 82.35%, negative predictive value = 81.81%).

Using this cut-off value, tubular proteinuria was diagnosed in 10 dogs (35.71%), non-tubular proteinuria in 17 animals (60.71%), and one dog (3.57%) had normal protein excretion. The uAPR results showed a high correlation with the electrophoresis outcomes. There was only one dog with a false negative result (in the treated group), and 3 dogs had false positive results with normal protein excretion pattern on electrophoresis (2 laboratory beagles and one dog of the non-treated group).

Based on the results of this study we suggest that uAPR could be a simple and affordable method to identify the source of proteinuria, thus the determination of uAPR may help in the diagnostic and therapeutic decision-making in proteinuric dogs.