Diagnostic accuracy of refractometry methods for estimating passive immunity status in neonatal beef calves.

BACKGROUND: Assessing the inadequate transfer of passive immunity (ITPI) in beef calves is crucial because calves with ITPI are at high risk for morbidity and mortality. OBJECTIVES: The aim of this study was to determine the accuracy of digital Brix (D-BRIX) and digital serum total protein (D-STP) refractometers to estimate different passive immunity status in beef calves and to determine the robustness of thresholds. METHODS: Blood samples were collected from 202 (1-7 days old) beef calves. Serum total solid percentages, total protein concentrations, and IgG concentrations were measured with the D-BRIX refractometer, D-STP refractometer, and gold standard radial immunodiffusion (RID) assay, respectively. Data were analyzed using diagnostic test accuracy, areas under the receiver operating characteristics curve, Cohen's kappa coefficient, and misclassification costs analysis to estimate IgG concentrations <10, <16, and <24 mg/mL. RESULTS: For the prediction of serum IgG concentrations <10, <16 and <24 mg/mL, the optimal cut-off values were determined to be <8.5% (Se: 100.0% (95% CI: 87.9-100.0); Sp: 94.2% [95% CI: 89.6-97.2]), <8.5% (Se: 92.1% [95% CI: 78.6-98.2]; Sp: 97.6% [95% CI: 93.9-99.3]), and <10.1% (Se: 88.8% [95% CI: 79.7-94.7]; Sp: 67.2% [95% CI: 58.1-75.4]), respectively, for the D-BRIX refractometer; and <5.2 g/dL (Se: 100.0% [95% CI: 87.9-100.0]; Sp: 93.6% [95% CI: 88.9-96.8]), <5.2 g/dL (Se: 92.1% [95% CI: 78.6-98.2]; Sp: 97.0% [95% CI: 93.0-99.0]), and <6.4 g/dL (Se: 87.5% [95% CI: 78.2-93.8]; Sp: 69.7% [95% CI: 60.7-77.7]), respectively, for the D-STP refractometer. CONCLUSIONS: The digital Brix and digital serum total protein refractometers can be used as monitoring tools for assessing passive immunity transfer in neonatal beef calves.

Diagnostic accuracy of digital Brix and serum total protein refractometers in estimating different passive immunity levels in dairy calves.

The aim of this study was to determine the diagnostic accuracy of digital serum total protein (TP) and digital Brix refractometers in estimating different passive immunity levels (<10, <18, <25 mg/mL) in dairy calves. Blood samples were collected from 260 apparently healthy Holstein calves, aged 2-7 days. Serum IgG concentrations were measured using digital Brix and TP refractometers and the radial immunodiffusion (RID) assay, as the gold standard. Data were analyzed by a receiver operating characteristics (ROC) analysis, the area under the ROC curves (AUC) and Cohen's kappa (κ). Optimal thresholds were determined as < 8.4, < 9.0 and < 9.4% for the digital Brix refractometer, and < 5.0, < 5.4 and < 5.8 g/dL for the serum TP refractometer in estimating IgG concentrations of < 10, < 18, < 25 mg/mL, respectively. The sensitivity (Se) and specificity (Sp) of the Brix refractometer were 96.3% and 88.8% for < 8.4% Brix, 97.0% and 83.4% for < 9.0% Brix, and 85.5% and 77.8% for < 9.4% Brix, respectively. The Se and Sp of the serum TP refractometer were 96.3% and 90.1% for < 5.0 g/dL, 91.0% and 89.6% for < 5.4 g/dL, 79.6% and 85.2% for < 5.8 g/dL, respectively. The discriminant ability of the refractometers was moderately accurate in estimating IgG concentrations of < 10 and < 18 mg/mL, and highly accurate in estimating IgG concentrations of < 25 mg/mL. Both refractometers substantially agreed with RID-IgG results and almost perfectly agreed with each other. In conclusion, the digital Brix and digital serum TP refractometers offer a good utility for determining different passive immunity levels in dairy calves.