Prevalence of insulin dysregulation in a sport horse population as determined by traditional and stall‐side testing

BACKGROUND: The prevalence of insulin dysregulation (ID) has not been investigated in sport horses. Stall-side insulin assays offer convenience but need further validation. OBJECTIVES: To determine the prevalence of and risk factors for ID in a sport horse population using an oral sugar test (OST) and assess agreement between stall-side and validated laboratory assays for insulin quantification. STUDY DESIGN: Prospective cross-sectional study. METHODS: One hundred eighty sport horses presenting for orthopaedic evaluation at a university hospital (N = 140) or local farms (N = 40) were tested for ID using OST (0.15 mL/kg light corn syrup). Morphometric data were collected, and baseline serum leptin and adiponectin concentrations were measured. Insulin concentrations were measured using the validated fluorescence enzyme immunoassay (FEIA) and a stall-side lateral flow assay (LFA). ID was diagnosed if FEIA insulin measured >20 μIU/mL at T0 or >30 μIU/mL at T60/T90. Factors associated with ID were assessed using a mixed effects binary logistic regression model. Assay agreement was assessed using Pearson's correlation coefficient and Bland-Altman plot. Receiver operator characteristic curve analysis was performed to determine diagnostic cut-offs for LFA. RESULTS: ID was diagnosed in 22.8% (41/180) of horses. Only 11/41 ID horses had increased fasted insulin. Increasing leptin/adiponectin ratio in males was the only significant predictor of ID (OR = 1.102, 95% CI 1.036-1.171). Correlation between FEIA and LFA insulin measures was good (r = 0.81, 95% CI 0.78-0.84), but the LFA read on average 13.62 μIU/mL higher than the FEIA and had greater variability at higher insulin concentrations. Area under the ROC curve showed the LFA was excellent at correctly classifying ID status (AUC = 0.95, 95% CI 0.93-0.97). MAIN LIMITATIONS: Single-centre study, voluntary enrolment may overestimate ID prevalence. CONCLUSIONS: ID is common in sport horses and often requires dynamic insulin testing to diagnose. Physical appearance does not predict ID risk. Agreement between stall-side and laboratory assays is good.