Effect of blood contamination on results of dipstick evaluation and urine protein-to-urine creatinine ratio for urine samples from dogs and cats

Abstract

OBJECTIVE To evaluate effects of blood contamination on dipstick results, specific gravity (SG), and urine protein-to-urine creatinine ratio (UPCR) for urine samples from dogs and cats. SAMPLE Urine samples collected from 279 dogs and 120 cats. PROCEDURES Urine pools were made for each species (dogs [n = 60] and cats [30]). Blood was added to an aliquot of a pool, and serial dilutions were prepared with the remaining urine. Color and dipstick variables were recorded, and SG and UPCR were measured. For cats, 1 set of pools was used; for dogs, 2 sets were used. Comparisons were made between undiluted urine and spiked urine samples for individual colors. Repeated-measures ANOVA on ranks was used to compare dipstick scores and UPCR results; χ tests were used to compare proteinuria categorizations (nonproteinuric, borderline, or proteinuric). RESULTS Any blood in the urine resulted in significantly increased dipstick scores for blood. In both species, scores for bilirubin and ketones, pH, and SG were affected by visible blood contamination. No significant difference for the dipstick protein reagent results was evident until a sample was visibly hematuric. The UPCR was significantly increased in dark yellow samples of both species. Proteinuria categorizations differed significantly between undiluted urine and urine of all colors, except light yellow. CONCLUSIONS AND CLINICAL RELEVANCE Any degree of blood contamination affected results of dipstick analysis. Effects depended on urine color and the variable measured. Microscopic blood contamination may affect the UPCR; thus, blood contamination may be a differential diagnosis for proteinuria in yellow urine samples.

Relationships among urinary protein‐to‐creatinine ratio, urine specific gravity, and bacteriuria in canine urine samples

“…Various studies have evaluated the effect of active urine sediment findings on UP : C. Increases in UP : C have been demonstrated after gross and microscopic blood contamination. Another study demonstrated the potential for macroscopic hematuria to lead to increased urinary albumin concentrations .…”

Urine creatinine concentration and urine protein‐to‐creatinine ratios in healthy nonracing Greyhounds

“…When outliers were excluded, the upper reference limit was 0. 23,24 Other abnormalities that could potentially cause high UPCs, such as pyuria, 25,26 were not observed in the outlier samples.…”

“…Dogs identified as outliers were examined for potential causes of the increased UPCs. Two Greyhounds had trace or 1+ positive hemoglobin results on dipstick analyses; however, urine samples with grossly indistinguishable blood contamination were not excluded because several studies have shown that mild blood contamination (that is not evident grossly) had no significant effect on UPCs 23,24 . Other abnormalities that could potentially cause high UPCs, such as pyuria, 25,26 were not observed in the outlier samples.…”

Evaluation of the effect of urine dip vs urine drip on multi‐test strip results

“…A further dog with ketoacidosis was positive for ketones on all testing. The presence of trace ketones was recently shown to be affected by the presence of blood; the single sample with the discrepancy in ketone readings had 80 cell/dL red blood cells recorded for all six readings taken. Therefore, the presence of the red blood cells could explain the ketones; alternatively, this single discrepant ketone reading could be due to ketone concentrations being close to the threshold for detection or due to the high acuity of the analyzer, especially for ketones …”