Comparison of turbidometric immunoassay, refractometry, and gamma‐glutamyl transferase to radial immunodiffusion for assessment of transfer of passive immunity …

AJ Kreuder, RM Breuer, C Wiley… - Journal of Veterinary …, 2023 - Wiley Online Library
AJ Kreuder, RM Breuer, C Wiley, T Dohlman, JS Smith, L McKeen
Journal of Veterinary Internal Medicine, 2023Wiley Online Library
Background Attainment of adequate transfer of passive immunity (TPI) is critical to health of
calves; however, studies comparing available tools for measurement of TPI in individual
beef animals are limited. Objectives To report agreement between 4 tests evaluating
individual TPI status in beef calves. Animals One hundred ninety‐six beef calves born to
cows and heifers presenting for calving management or dystocia. Methods Retrospective
study to assess serum immunoglobulin (IgG) concentrations via turbidimetric immunoassay …
Background
Attainment of adequate transfer of passive immunity (TPI) is critical to health of calves; however, studies comparing available tools for measurement of TPI in individual beef animals are limited.
Objectives
To report agreement between 4 tests evaluating individual TPI status in beef calves.
Animals
One hundred ninety‐six beef calves born to cows and heifers presenting for calving management or dystocia.
Methods
Retrospective study to assess serum immunoglobulin (IgG) concentrations via turbidimetric immunoassay (TI), gamma‐glutamyl transferase (GGT), serum total protein (TP), and single radial immunodiffusion (RID; reference standard). Test agreement was evaluated using Passing‐Bablok regression, Bland‐Altman analysis, Cohen's kappa, and receiver operating characteristic (ROC) curves with and without covariate adjustment to determine optimal thresholds.
Results
Correlation between RID and test results varied: TI, ρ = 0.757; TP, ρ = 0.715; GGT: ρ = 0.413. For the TI compared to RID, regression analysis identified a constant (intercept = −0.51 [CI: −2.63, 3.05]) and proportional (slope = 1.87 [CI: 1.69, 2.08]) bias. Based on ROC, TI concentrations of ≤9.89 and ≤13.76 g/L, and TP concentrations of ≤5.5 and ≤6.0 g/dL, indicated IgG concentrations <18.0 and <25.0 g/L, respectively.
Conclusions and Clinical Importance
Within this cohort of calves, TI demonstrated the best correlation with RID; however, significant bias was identified which led to frequent underestimation of IgG concentration. Serum total protein demonstrated less correlation with RID but had less misclassification than TI. Both TI and TP demonstrated less correlation for calves that received colostrum replacement prompting clinical awareness of colostrum type when evaluating individual TPI in beef calves.
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