Department of Production Animal Health, University of Calgary Faculty of Veterinary Medicine, Calgary, Alberta, Canada.
Department of Animal Medicine, Division of Infectious Diseases, Faculty of Veterinary Medicine, Zagazig University, Zagazig, Egypt.
J Vet Intern Med. 2021 Jan;35(1):632-643. doi: 10.1111/jvim.16016. Epub 2020 Dec 23.
Refractometry is used to assess transfer of passive immunity (TPI), but studies evaluating different refractometers and appropriate thresholds for recommended target immunoglobulin G (IgG) concentrations for beef calves are limited.
To evaluate test performance of digital (DSTP) and optical (OSTP) serum total protein (STP) refractometers and a digital Brix (DBRIX) refractometer for assessment of passive immunity in beef calves.
A total of 398 beef calves from 6 herds, 1 to 7 days of age.
Serum IgG concentration was estimated by DSTP, OSTP, and DBRIX, and measured by radial immunodiffusion (RID). Correlation coefficients (r) among results were calculated. Optimal STP and Brix thresholds for identification of IgG <10, <16, and <24 g/L were determined using interval likelihood ratios. Refractometer performance and agreement were assessed using areas under the curve (AUC), diagnostic test characteristics, Cohen's kappa (κ), and Bland-Altman analysis.
Refractometer results were highly correlated with RID (r = 0.82-0.91) and with each other (r = 0.91-0.95), and overall test performance was excellent (AUC = 0.93-0.99). The STP concentrations of ≤5.1, ≤5.1, and ≤5.7 g/dL and Brix percentages of ≤7.9%, ≤8.3%, and ≤8.7% indicated IgG concentrations <10, <16, and <24 g/L, respectively. Agreement of refractometers with RID was variable (κ = 0.46-0.80) and among refractometers was substantial (κ = 0.62-0.89).
All refractometers showed good utility as monitoring tools for assessment of TPI in beef calves.
折射仪用于评估被动免疫转移（TPI），但评估不同折射仪和推荐的肉牛免疫球蛋白 G（IgG）浓度目标值的适当阈值的研究有限。
评估数字（DSTP）和光学（OSTP）血清总蛋白（STP）折射仪以及数字 Brix（DBRIX）折射仪在评估肉牛被动免疫中的测试性能。
来自 6 个牛群的 398 头 1 至 7 日龄的肉牛。
通过 DSTP、OSTP 和 DBRIX 估计血清 IgG 浓度，并通过放射免疫扩散（RID）进行测量。计算结果之间的相关系数（r）。使用间隔似然比确定用于识别 IgG <10、<16 和 <24 g/L 的最佳 STP 和 Brix 阈值。使用曲线下面积（AUC）、诊断测试特征、Cohen's kappa（κ）和 Bland-Altman 分析评估折射仪性能和一致性。
折射仪结果与 RID 高度相关（r = 0.82-0.91），彼此之间也高度相关（r = 0.91-0.95），整体测试性能非常出色（AUC = 0.93-0.99）。STP 浓度≤5.1、≤5.1 和≤5.7 g/dL 和 Brix 百分比≤7.9%、≤8.3% 和≤8.7% 分别表示 IgG 浓度<10、<16 和<24 g/L。折射仪与 RID 的一致性差异很大（κ = 0.46-0.80），而折射仪之间的一致性很高（κ = 0.62-0.89）。
所有折射仪均显示出良好的监测工具，可用于评估肉牛的 TPI。
