E15 - Evaluation of a Lateral Flow Assay for Failure of Passive Transfer Diagnosis in Crias/Foals

Abstract:

Background: Serum immunoglobulin G (IgG) measurement is used for assessing passive transfer of immunity in foals and crias, with concentrations < 800mg/dl and < 1000mg/dl indicating failure of transfer of passive immunity (FTPI), respectively. Hypothesis/

Objectives: Evaluate the accuracy and precision of a stall-side lateral flow assay (LFA) for FTPI diagnosis in foals and crias. Animals: Serum from 50 foals and 38 crias were analyzed with the LFA and “gold standard” laboratory immunoturbidometric assay (ITA).

Methods: Associations between assays, median assay concentrations and the difference between assays were determined using Spearman rank correlation (Rsp), Wilcoxon signed-rank test, and a Bland-Altman plot, respectively. Precision was determined by calculating the coefficient of variation (CV) of 5 replicate values of 3 different IgG concentrations. Accuracy for FTPI diagnosis was calculated as the percentage of neonates with LFA results below designated cut-offs.

Results: There was moderate to good correlation between IgG LFA and ITA concentrations in foals (Rsp=0.740, p=0.001) and crias (Rsp=0.809, p< 0.001). However, compared to the ITA, median LFA IgG concentrations were significantly lower in foals (LFA: 799mg/dL, ITA: 1036mg/dL, p=0.002; median bias: -198mg/dL) and higher in crias (LFA: 3000mg/dL; ITA: 850mg/dL, p=< 0.001; median bias: 1155mg/dL). Replicate analysis with the LFA yielded high variation (CV: 27-49% in foals, 42-66% in crias). Of 16 foals and 23 crias with ITA concentrations below the FTPI cut-off, 88% of foals and 48% of crias would have an FTPI diagnosis with the LFA. Conclusion/Clinical Importance: The stall-side LFA should not be used to diagnose FTPI in foals or crias.