Validation of a stall-side Immunoglobin 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 exposure and sepsis. Laboratory RID and immunoturbidimetric assays quantify IgG present in a foal sample but are time-consuming. 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 IgG), 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: Sidekick IgG test assessed with serial diluted foal sample (0-2000mg/dL, three replicates). Sidekick IgG compared to RID and Immunoturbidimetric assay. Serum/plasma samples from 10 foals created two cohorts, one representing successful passive transfer and one failed passive transfer. Agreement in IgG quantification between matched blood and plasma samples by the Sidekick IgG was tested for three foals. Results: Sidekick IgG test showed excellent recovery and high repeatability, 96.3% - 109.5% across clinically relevant range of 400-800mg/dL (CV% 3.7-10). Overall strong agreement with reference methods RID and Immunoturbidimetric assay. Strong agreement between matched whole-blood and plasma samples. Main Limitations: Small cohort (10 foals) Conclusions: Traditional laboratory-based assays have limitations such as need for specialised instrumentation, laboratory infrastructure, and skilled technical personnel. This is incompatible with the time-sensitive nature of many interventions and are particularly relevant in ambulatory or field-based equine practice, where access to laboratory services may be restricted. The stall-side Sidekick IgG assay 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.