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

BACKGROUND: Repeatability of the oral sugar test (OST) has not been evaluated.

OBJECTIVES: We 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.

ANIMALS: Fifty-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.

METHODS: Two 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.

RESULTS: No 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 IMPORTANCE: Repeatability 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.