title: Use of the oral sugar test in ponies when performed with or without prior fasting.
abstract: BACKGROUND
  It is recommended that the oral sugar test (OST) for insulin dysregulation (ID) be performed after an overnight fast, but fasting is impractical in ponies kept solely at pasture. There are few data on OST repeatability and reliability in ponies.
  
  
  OBJECTIVE
  To report 1) whether OST results obtained in the morning after an overnight fast or without fasting in the afternoon (FASTING/FED) can be used interchangeably, 2) time of highest insulin concentration Tmax[insulin], repeatability and reliability of insulin response to the OST when FASTING or FED and 3) dichotomous agreement (ID/normal) within a small sample when FASTING or FED.
  
  
  METHODS
  Method comparison study.
  
  
  METHODS
  Oral sugar tests were performed on four occasions in 10 adult native British ponies, twice FASTING and twice FED. Insulin concentrations were measured by radioimmunoassay at 0-120 min (T0,30,60,75,90,120). Differences between FASTING and FED results were assessed using mixed effects models. Indices of repeatability and reliability were calculated; dichotomous agreement was reported using kappa statistics.
  
  
  RESULTS
  Serum [insulin] was significantly (P≤0.05) higher at T60-T90with prior fasting (estimated differences [95% confidence intervals]): T60: 23.5 μiu/ml (8.7-38.4 μiu/ml), T75: 27.1 μiu/ml (12.3-41.8 μiu/ml), T90: 15.1 (0.36-29.9 μiu/ml). Most frequently, Tmax[ins] occurred at T30. At any single time point, within-subject coefficients of variation were: FASTING: 40% and FED: 31%. The 95% limits for repeatability were FASTING: 29-340%, FED: 41-240%. Test reliabilities were FASTING: 0.70 and FED: 0.67. For dichotomous interpretation similar results (kappa = 0.7) were obtained using cut-offs of [Insulin] >60 μiu/ml at T60or T90for FASTING and [Insulin] >51 μiu/ml at T30or T60for FED samples.
  
  
  CONCLUSIONS
  Oral sugar tests were performed on a small number of animals on one pasture during one season (spring).
  
  
  CONCLUSIONS
  Clinicians should beware of interpreting changes in absolute OST results owing to poor repeatability. When stabling is unavailable, OSTs of ponies at pasture may yield similar dichotomous results without prior fasting.
authors.affiliation: Department of Clinical Sciences and Services, Royal Veterinary College, London, UK.|Bell Equine Veterinary Clinic, Mereworth, Kent, UK.
authors.forename: E J
authors.initials: EJ
authors.lastname: Knowles
authors.affiliation: Equine Studies Group, WALTHAM Centre for Pet Nutrition, Waltham on the Wolds, Leicestershire, UK.
authors.forename: P A
authors.initials: PA
authors.lastname: Harris
authors.affiliation: Department of Comparative Biomedical Sciences, Royal Veterinary College, London, UK.
authors.forename: J
authors.initials: J
authors.lastname: Elliott
authors.affiliation: Department of Clinical Sciences and Services, Royal Veterinary College, London, UK.
authors.forename: N J
authors.initials: NJ
authors.lastname: Menzies-Gow
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D005215:Fasting / Q000378:metabolism*; D005951:Glucose Tolerance Test / Q000379:methods / Q000662:veterinary*; D006736:Horses / Q000378:metabolism*; D006946:Hyperinsulinism; D007328:Insulin / Q000378:metabolism; D015203:Reproducibility of Results; D012621:Seasons
chemical_list: D001786:Blood Glucose; D007328:Insulin
keywords: 
  EMS
  ; endocrine; horse; insulin; laminitis