The effect of urea on refractometric total protein measurement in dogs and cats with azotemia

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 me...

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Bibliographic Details
Published in:Veterinary clinical pathology 2017-03, Vol.46 (1), p.138-142
Main Authors: Legendre, Kelsey P., Leissinger, Mary, Le Donne, Viviana, Grasperge, Britton J., Gaunt, Stephen D.
Format: Article
Language:English
Subjects:
Animals
Assaying
Azotemia - blood
Azotemia - veterinary
Bias
Bilirubin - blood
Biuret
Blood levels
Blood Proteins - analysis
BUN
cat
Cat Diseases - blood
Cats
dog
Dog Diseases - blood
Dogs
Error analysis
interference
Prospective Studies
Proteins
Refraction
refractometer
Refractometry - veterinary
Spectrophotometry - veterinary
Statistical analysis
total protein
Urea
Urea - blood
Veterinary medicine
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Summary: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 
ISSN:0275-6382
1939-165X
DOI:10.1111/vcp.12464