BackgroundRepeatability of the oral sugar test (OST) has not been evaluated.ObjectivesWe hypothesized that OST glucose, insulin, active (aGLP‐1) and total (tGLP‐1) glucagon‐like peptide 1, and high‐molecular‐weight (HMW) adiponectin results would be repeatable.AnimalsFifty‐three horses from a Tennessee research facility (n = 23) and private practice in Missouri (n = 30), including animals with medical histories of equine metabolic syndrome.MethodsTwo OSTs were performed 7–14 days apart and plasma glucose and insulin concentrations were measured at 0, 60, and 75 minutes; a positive result was defined as detection of an insulin concentration >45 μU/mL at 60 or 75 minutes. Plasma aGLP‐1 and serum tGLP‐1 concentrations at 75 minutes and serum HMW adiponectin concentrations at 0 minute were measured in the Missouri group. Bland‐Altman analyses were performed.ResultsNo adverse events were reported. Bland‐Altman analysis indicated mean ± SD bias of 1.5 ± 14.8 μU/mL (95% confidence interval [CI], −27.6 to 30.5 μU/mL) and 1.2 ± 16.1 μU/mL (95% CI, −30.4 to 32.8 μU/mL) for insulin concentrations at 60 and 75 minutes, respectively. There was 91 and 83% agreement in test interpretation between test days for OST insulin results for all horses in the Tennessee and Missouri groups, respectively.Conclusions and Clinical ImportanceRepeatability of the OST was acceptable when values obtained from Bland‐Altman analyses were evaluated, and there was good agreement in binary (negative/positive) test interpretation for insulin concentrations. However, wide 95% CIs were detected for insulin concentrations.
Background: Determination of adrenocorticotropic hormone (ACTH) concentration is a commonly used test in the evaluation of endocrine causes of equine laminitis, but the concentration in healthy horses can be high at certain times of year, which alters the specificity of the ACTH test.Objective: To determine if circulating concentrations of ACTH, cortisol, glucose, insulin, and thyroxine vary month to month in healthy horses and in horses with equine metabolic syndrome (EMS).Animals: Nine healthy adult horses were studied on their farm/stable over the course of 1 year. After the diagnosis of EMS, 10 laminitic horses residing at the same farm/stable were also studied.Methods: Prospective study of healthy and laminitic horses. Plasma/serum samples were analyzed for concentrations of hormones and glucose.Results: ACTH was the only analyte to show a discrete seasonal pattern, with concentrations in healthy and EMS horses frequently outside of the reference range (9-35 pg/mL) in August through October. Insulin was elevated (440 mIU/mL) in EMS horses during most months and median serum glucose was generally higher in EMS horses (100 mg/dL, range, 76-163 mg/ dL) than in controls (94 mg/dL, range, 56-110 mg/dL), but no seasonal patterns for insulin or glucose were found.Conclusions and Clinical Importance: An increased ACTH concentration in horses in late summer or autumn should be interpreted with caution. In contrast, insulin concentration is maintained within the reference range throughout the year in healthy horses, thus an increased insulin concentration at any time of year should raise suspicions of EMS, ECD, or both.
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