Repeatability of Oral Sugar Test Results, Glucagon‐Like Peptide‐1 Measurements, and Serum High‐Molecular‐Weight Adiponectin Concentrations in Horses

Abstract

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.

Effect of varying the dose of corn syrup on the insulin and glucose response to the oral sugar test

“…A previous study found within subject agreement for a single sample to be moderate to fair, with the same animal having varying response at the same time point . A study using larger numbers of animals (n = 53) found the agreement to be good at 60 and 75 min . AUC i was more repeatable in the present study than a single time point.…”

“…Although testing was undertaken up to 120 min in this current study, no further blood samples were taken beyond that point; therefore, it is not possible to state whether a difference would have been seen at 180 min. However, a more recently published study with larger numbers, found no significant difference in glucose response between insulin dysregulated and normal animals at time 0–75 min on two occasions. It is surprising that the dose relationship in this study was not incremental in that 0.45 mL/kg BW dose did not lead to a significantly higher glucose response than the 0.3 mL/kg BW dose.…”

Use of the oral sugar test in ponies when performed with or without prior fasting

“…One study [2] reported a high coefficient of variation (CV) (45%) for the insulin area under the curve (AUC Insulin ). Another reported a lower median CV (15.3%) but a wide range (0.3-78.5%) of individual horse CVs [9].…”

Repeatability of the hyperglycaemic clamp for assessment of β‐cell response and insulin sensitivity in horses

“…For example, based on the CR for Insulin 60–120 , a horse needs to have a change of at least 14.5 μIU/mL at re‐assessment in order to have 95% confidence that the change has clinical relevance. In comparison, horses with normal insulin regulation are reported to have CR of 38.7 μIU/mL for single samples of plasma insulin taken at 60 min of an OST . These CRs are thus absolute index values for repeatability with the same unit but they are not directly comparable with each other.…”