Variability of first morning urine specific gravity in 103 healthy dogs

Abstract

Background Urine specific gravity (USG) is an integral part of the urinalysis and a key component of many clinical decisions, and fluctuations in USG have the potential to impact case management. Objectives To determine the intraindividual variability of first morning USG results in healthy dogs. Animals One hundred three healthy client‐owned dogs. Methods Dogs were deemed healthy based on clinical history and physical examination findings. Repeated USG measurements were performed over the course of 2 weeks. Three urine samples were collected each week for a total of 6 samples per dog. Sample collection was distributed evenly throughout the week. Urine samples were acquired immediately upon waking and before any ingestion of liquids, food, or exertion of physical activity in the dogs. All measurements were made using the same Misco digital refractometer. Results Intraindividual USG was variable over the course of the study. The mean difference between the minimum and maximum USG for each dog was 0.015 (SD, 0.007). The within‐week difference between the minimum and maximum USG was less than over the complete 2‐week study (0.009 [SD 0.006] for week 1 and 0.010 [SD 0.007] for week 2). The mean coefficient of variance across all 6 time points was 15.4% (SD 8.97%). Conclusions and Clinical Importance Clinically important variation occurs in USG in healthy animals and might impact clinical decision‐making when diagnostic cutoff points are utilized. Clinicians should be aware of inherent variability in this clinical variable when analyzing results.

Environmental chemical exposures in the urine of dogs and people sharing the same households

“…We normalized all urinary analytes to urine creatinine to control for individual and species differences in urine concentration. Median urine creatinine was higher in dogs, which is consistent with the dog's higher urine concentrating ability compared to humans [26,27]. This normalization should not have affected our conclusions because correction for creatinine should lead to lower concentrations in dogs relative to humans, not the relatively higher concentrations that we observed.…”

“…The median urine volume submitted was 40 ml for dogs (range 5-175 ml) and 100 ml for human participants (range 35-250 ml). Urine creatinine was higher in dogs (median 204 mg/dl, range 35-263 mg/dl) compared to humans (median 90 mg/dl, range 15-176 mg/dl), as expected based on higher urine concentrating ability in dogs compared to humans [26,27].…”

“…Median urine creatinine was higher in dogs, which is consistent with the dog's higher urine concentrating ability compared to humans. 26,27 This normalization should not have affected our conclusions because correction for creatinine should lead to lower concentrations in dogs relative to humans, not the relatively higher concentrations that we observed. However, urine creatinine in people can vary by sex, age and ethnicity, 48 and while this should have been a minor variable in our population of mostly Caucasian women, urine specific gravity should be incorporated as an additional normalization factor in future studies.…”

“…Urine creatinine was higher in dogs (median 204 mg/dL, range 35-263 mg/dL) compared to humans (median 90 mg/dL, range 15-176 mg/dL), as expected based on higher urine concentrating ability in dogs compared to humans. 26,27 The acrolein metabolite 3-HPMA was quantifiable in all urine samples, with wide variability in concentrations among humans and dogs as adjusted for urine creatinine (Figure 1A). Median 3-HPMA/cr concentrations were significantly higher in dogs (1269 ng/mg) compared to humans (285 ng/mg; P < 0.0001), and a median 4.9-fold higher between individual dogs and their owners (range 0.6 -24.8-fold).…”

Interobserver reliability of canine urine specific gravity assessed by analog or digital refractometers

“…9,11,14,15 These sources of variation are in addition to the day-to-day variation that can be observed within individual animals as a result of daily variation in hydration status and environment. 10…”