Legendre Kelsey P, Leissinger Mary, Le Donne Viviana, Grasperge Britton J, Gaunt Stephen D
Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA.
Finn Pathologists - CVS Diagnostic Laboratories, Harleston, Norfolk, UK.
Vet Clin Pathol. 2017 Mar;46(1):138-142. doi: 10.1111/vcp.12464. Epub 2017 Feb 27.
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.
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.
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.
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.
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.
虽然蛋白质是血浆或血清中通过折射仪测量的主要溶质，但非蛋白质物质也会影响折射角度。与双缩脲法相比，目前文献中对于哪些非蛋白质物质会导致折射法测定的总蛋白出现人为偏高存在争议。
本研究旨在确定氮质血症动物（特别是血尿素浓度升高的动物）的血液，与通过双缩脲法测定的总蛋白浓度相比，其折射法测定的总蛋白浓度是否会显著更高。
通过收集氮质血症犬猫（n = 26）和非氮质血症犬猫（n = 34）的数据进行前瞻性病例系列研究。此外，进行了一项体外研究，向强化电解质溶液中添加不同浓度的尿素，并用折射仪和分光光度计评估总蛋白。进行统计分析以确定尿素的影响。
与双缩脲法测定的蛋白相比，两组中折射法测定的总蛋白均显示出正偏差，但氮质血症组的偏差高于非氮质血症组。非氮质血症组总蛋白测量的平均差异（0.59 g/dL）显著低于（P <.01）氮质血症组的平均差异（0.95 g/dL）。体外实验显示存在正偏差和比例误差。
本研究表明，无论是在体内还是体外，与双缩脲法相比，尿素浓度的增加会显著提高折射仪测量的总蛋白浓度。
