title: Use of proxies and reference quintiles obtained from minimal model analysis for determination of insulin sensitivity and pancreatic beta-cell responsiveness in horses.
abstract: OBJECTIVE
  To develop proxies calculated from basal plasma glucose and insulin concentrations that predict insulin sensitivity (SI; L.min(-1) x mU(-1)) and beta-cell responsiveness (ie, acute insulin response to glucose [AIRg]; mU/L x min(-1)) and to determine reference quintiles for these and minimal model variables.
  
  
  METHODS
  1 laminitic pony and 46 healthy horses.
  
  
  METHODS
  Basal plasma glucose (mg/dL) and insulin (mU/L) concentrations were determined from blood samples obtained between 8:00 AM and 9:00 AM. Minimal model results for 46 horses were compared by equivalence testing with proxies for screening SI and pancreatic beta-cell responsiveness in humans and with 2 new proxies for screening in horses (ie, reciprocal of the square root of insulin [RISQI] and modified insulin-to-glucose ratio [MIRG]).
  
  
  RESULTS
  Best predictors of SI and AIRg were RISQI (r = 0.77) and MIRG (r = 0.75) as follows: SI = 7.93(RISQI) - 1.03 and AIRg = 70.1(MIRG) - 13.8, where RISQI equals plasma insulin concentration(-0.5) and MIRG equals [800 - 0.30(plasma insulin concentration 50)(2)]/(plasma glucose concentration - 30). Total predictive powers were 78% and 80% for RISQI and MIRG, respectively. Reference ranges and quintiles for a population of healthy horses were calculated nonparametrically.
  
  
  CONCLUSIONS
  Proxies for screening SI and pancreatic beta-cell responsiveness in horses from this study compared favorably with proxies used effectively for humans. Combined use of RISQI and MIRG will enable differentiation between compensated and uncompensated insulin resistance. The sample size of our study allowed for determination of sound reference range values and quintiles for healthy horses.
authors.affiliation: Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0306, USA.
authors.forename: Kibby H
authors.initials: KH
authors.lastname: Treiber
authors.forename: David S
authors.initials: DS
authors.lastname: Kronfeld
authors.forename: Tanja M
authors.initials: TM
authors.lastname: Hess
authors.forename: Ray C
authors.initials: RC
authors.lastname: Boston
authors.forename: Pat A
authors.initials: PA
authors.lastname: Harris
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000097:blood*; D001786:Blood Glucose; D006736:Horses / Q000097:blood*; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology*; D050417:Insulin-Secreting Cells / Q000502:physiology*; D008954:Models, Biological; D012015:Reference Standards
chemical_list: D015415:Biomarkers; D001786:Blood Glucose; D007328:Insulin