Validation of a stall‐side immunoglobulin assay for use in equine reproductive management

Background: Equine foals receive IgG from mare colostrum through passive transfer. Failure of passive transfer (FPT) is a significant risk to the foal's life, leaving them vulnerable to infection and sepsis. Radial Immunodiffusion (RID) and immunoturbidimetric assays quantify IgG present in a foal sample but require a laboratory to complete. Accurate, reproducible, stall‐side testing to rapidly quantify IgG would allow for expedited clinical decisions, with potential to improve equine foal care and survival. Objectives: To evaluate the analytical and clinical performance of a stall‐side IgG lateral‐flow test and reader (Sidekick), assessing its use as a point‐of‐care (POC) test to provide reliable results and agreement of IgG quantification with gold‐standard methods. Study Design: Retrospective cohort. Methods: Stall‐side LFD IgG test (Sidekick) was assessed with serial diluted foal sample (0.8–20 g/L, three replicates) and Stall‐side LFD was compared to RID and Immunoturbidimetric assay. Serum/plasma samples from 10 foals created two cohorts, one representing successful passive transfer and one representing failed passive transfer. Agreement in IgG quantification between matched blood and plasma samples by the stall‐side LFD was tested in three foals. Results: The Stall‐side LFD IgG test showed excellent recovery and high repeatability, 96.3%–109.5% across the clinically relevant range of 4–8 g/L (CV% 3.7–10). Overall, there was strong agreement with the reference method and strong agreement between matched whole‐blood and plasma samples. Main Limitations: Small cohort (10 foals). Conclusions: The stall‐side IgG assay (Sidekick) delivers repeatable results enabling on‐the‐spot decisions and reducing delays from sample processing, transport and result reporting, with potential to enable informed decision‐making on whether to initiate or continue treatment for a foal with FPT.