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

Abstract

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.

Keywords: Endocrinology; Equine metabolic syndrome; Insulin; Insulin dysregulation; Laminitis.

Figure 1

Median (range) plasma glucose (A) and insulin (B) concentrations measured during two oral sugar tests repeated within 14 days of one another in 53 horses. Data from the first (circles; solid line) and second (squares; dotted line) test days are displayed.

Figure 2

Bland‐Altman plots (difference versus average) of plasma glucose (A) and insulin (B) concentrations measured at 60 minutes during oral sugar tests repeated within 14 days of one another in 53 horses.

Figure 3

Bland‐Altman plots (difference versus average) of plasma glucose (A) and insulin (B) concentrations measured at 75 minutes during oral sugar tests repeated within 14 days of one another in 53 horses.