The effect of clinically relevant levels of blood contamination on the assessment of proteinuria in dogs by use of the urine protein to urine creatinine ratio

Abstract

AIMS: The purpose of this study is to clarify the effect of clinically relevant levels of blood contamination on proteinuria assessment, by use of the urine protein to creatinine ratio, in dogs.

METHODS: Normal urine samples with urine protein to urine creatinine ratio (UPC) <0.5 were collected from 11 healthy dogs. To simulate haematuria, blood from each dog was added to its own urine sample to make final urine concentrations ranging from 0 to 5% blood. Urine protein and creatinine were measured biochemically. Urine dipstick analysis, specific gravity by refractometry and microscopic sediment examination were also performed on every sample.

RESULTS: As the level of blood contamination in the samples increased, the UPC increased. However, all of the samples had a UPC less than 0.5 while the urine colour remained yellow (i.e. 0.2% blood contamination or less). When the blood contamination was greater and caused a visible colour change (i.e. peach to orange-red) the UPC of some urine samples increased above 0.5. The UPC did not increase above 1.0 in any dog until the sample was distinctly red in colour.

CONCLUSIONS AND CLINICAL RELEVANCE: Blood contamination of the urine that does not result in a visible change in colour of the urine sample from yellow will not substantially increase the UPC. As such, the UPC level in yellow urine, even in the presence of microscopic haematuria, can be considered valid. Therefore, the practice of discouraging measurement of UPC in animals with microscopic haematuria should be discontinued. However, macroscopic haemorrhage may increase the UPC of a urine sample above the normal range of <0.5. In this situation haematuria would need to be considered as a differential diagnosis for the proteinuria.