Evaluation of a lateral flow immunoassay for the quantitative measurement of immunoglobulin G in foals compared with radial immunodiffusion.

Overview

• This study evaluated the accuracy and reliability of a lateral flow immunoassay (LFIA) for measuring immunoglobulin G (IgG) levels in newborn foals to detect failure of transfer of passive immunity (FTPI), comparing it to the standard radial immunodiffusion (RID) method.
• The LFIA showed strong correlation with RID and demonstrated potential as a practical point-of-care screening tool for FTPI, though it is not a complete substitute for RID in precise quantitative measurements.

Background and Objective

• Newborn foals receive IgG antibodies from their mothers through colostrum, providing essential early immune protection.
• Failure of transfer of passive immunity (FTPI) happens when a foal does not acquire sufficient IgG, increasing the risk for infections and mortality.
• Timely diagnosis of FTPI is critical for appropriate treatment and management.
• Radial immunodiffusion (RID) is the reference standard for measuring IgG but is time-consuming and requires lab facilities.
• Lateral flow immunoassays (LFIAs) offer rapid, point-of-care testing but have not been thoroughly validated for foals.
• The study aimed to validate the diagnostic accuracy of a quantitative LFIA in measuring IgG concentrations in neonatal foals, benchmarked against RID.

Methods

• Sample Population: Forty-two neonatal foals were sampled within 24 hours after birth.
• Sample Types: Serum, plasma, and whole blood samples were collected for analysis.
• Testing Methods:
  • LFIA for quantitative IgG measurement.
  • RID as the reference standard IgG measurement.
  • SNAP-based ELISA also performed for comparison.
• Diagnostic Accuracy Evaluation:
  • Receiver Operating Characteristic (ROC) analysis to assess performance at clinically relevant RID threshold values (<400 mg/dL and ≤800 mg/dL), which define FTPI risk categories.
  • Correlations (R²) calculated between LFIA and RID results.
  • Bland-Altman analysis conducted to evaluate agreement and bias between methods.
  • Evaluation conformed with STARD (Standards for Reporting Diagnostic Accuracy Studies) guidelines.

Results

• Correlation:
  • LFIA IgG results showed strong correlation with RID results within the analytical range (100-1000 mg/dL), with an R² of 0.91, indicating excellent agreement in quantification.
• Linearity, Precision, and Accuracy:
  • The LFIA demonstrated good linearity across the measured range, ensuring consistent and reliable detection.
  • Precision tests showed repeatable results.
  • Accuracy was satisfactory when compared to RID.
• Diagnostic Performance:
  • ROC analysis yielded very high Area Under the Curve (AUC) values ranging from 0.988 to 1.000 across serum, plasma, and whole blood matrices.
  • These values indicate excellent diagnostic ability to discriminate between foals with and without FTPI.
  • Sensitivity and specificity were high, although confidence intervals were wide due to a limited number of foals with confirmed FTPI.
• Sample Matrices:
  • The LFIA performed well across different blood sample types, making it adaptable for practical clinical use.
• Bland-Altman Analysis:
  • Showed good agreement with RID but suggested that LFIA should not replace RID when precise quantification is needed.

Conclusions and Implications

• The quantitative LFIA offers a rapid, convenient, and reliable screening tool for identifying foals at risk of FTPI, which can facilitate early intervention.
• Strong agreement with RID supports LFIA use in clinical settings for initial classification of passive immunity status.
• LFIA is not interchangeable with RID for exact IgG quantification—RID remains necessary for detailed diagnostic confirmation.
• Given the limited number of FTPI-positive foals in this study, further research is advised to confirm performance in larger and more diverse populations.
• The LFIA’s ability to work with serum, plasma, and whole blood enhances its practical applicability in field or hospital environments.
• Integration of this LFIA in veterinary practice could improve timely detection and management of FTPI, reducing disease risk and mortality in neonatal foals.