Peer-reviewed veterinary case report
The effect of urea on refractometric total protein measurement in dogs and cats with azotemia.
- Journal:
- Veterinary clinical pathology
- Year:
- 2017
- Authors:
- Legendre, Kelsey P et al.
- Affiliation:
- Department of Pathobiological Sciences · United States
Plain-English summary
This study looked at how the presence of urea in the blood affects the measurement of total protein in dogs and cats with a condition called azotemia, which means they have high levels of waste products in their blood. Researchers compared two methods of measuring protein: a refractometer and a biuret assay. They found that the refractometer often showed higher protein levels in azotemic animals than the biuret assay did, and this difference was more pronounced in those with higher urea levels. The results suggest that when urea is present in larger amounts, it can lead to misleadingly high protein readings. Overall, the study concluded that urea significantly impacts protein measurements, which could be important for your pet's health assessments.
Abstract
BACKGROUND: While protein is the predominant solute measured in plasma or serum by a refractometer, nonprotein substances also contribute to the angle of refraction. There is debate in the current literature regarding which nonprotein substances cause factitiously high refractometric total protein measurements, as compared to the biuret assay. OBJECTIVES: The purpose of the study was to determine if the blood of azotemic animals, specifically with increased blood urea concentration, will have significantly higher refractometric total protein concentrations compared to the total protein concentrations measured by biuret assay. METHODS: A prospective case series was conducted by collecting data from azotemic (n = 26) and nonazotemic (n = 34) dogs and cats. In addition, an in vitro study was performed where urea was added to an enhanced electrolyte solution at increasing concentrations, and total protein was assessed by both the refractometer and spectrophotometer. Statistical analysis was performed to determine the effect of urea. RESULTS: The refractometric total protein measurement showed a positive bias when compared to the biuret protein measurement in both groups, but the bias was higher in the azotemic group vs the nonazotemic group. The mean difference in total protein measurements of the nonazotemic group (0.59 g/dL) was significantly less (P < .01) than the mean difference of the azotemic group (0.95 g/dL). The in vitro experiment revealed a positive bias with a proportional error. CONCLUSIONS: This study demonstrated that increasing concentrations of urea significantly increased the total protein concentration measured by the refractometer as compared to the biuret assay, both in vivo and in vitro.
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Search related cases →Original publication: https://pubmed.ncbi.nlm.nih.gov/28240785/