Diagnostic evaluation of insulin and glucose dynamics in light-breed horses receiving dexamethasone

Objective Insulin dysregulation is a hallmark of equine metabolic syndrome (EMS) and increases the risk for development of laminitis. Accurate diagnosis of insulin dysregulation is crucial for implementation of preventative strategies in this population. The objective was to assess the effects of dexamethasone administration on insulin and glucose dynamics in light-breed horses and assess the agreement of various diagnostic tests for insulin dysregulation [basal [insulin] (BI), oral sugar test (OST), and combined glucose-insulin test (CGIT)]. Animal Fourteen adult light-breed horses. Procedure Prospective, experimental study to assess insulin and glucose dynamics by performing basal insulin, OST, and CGIT before (baseline) and post-dexamethasone administration (0.08 mg/kg, PO, q24h) for 7 d. Insulin and glucose dynamics were assessed by the BI, OST, CGIT, and insulin sensitivity proxy measurements (RISQI, QUICKI, FGIR, HOMA-IR, IG) at the baseline and post-dexamethasone time points. Results The OST area under the insulin and glucose curves were increased following dexamethasone treatment (P < 0.001 and P < 0.01, respectively). Basal insulin, OST [ insulin] at 60 min and CGIT [ insulin] at 45 min were increased at the post-dexamethasone time point (P < 0.001, < 0.001, and < 0.01). Similarly, time spent in the positive glucose phase during the CGIT was longer at the post-dexamethasone time point (P < 0.001). The proxy measurements for insulin sensitivity (RISQI, QUICKI, FGIR) were decreased (P < 0.01) and the proxy measurements for insulin resistance (HOMA- IR) and beta-cell function (IG) were increased after dexamethasone administration (P < 0.01). More horses were classified with following dexamethasone administration, based on the diagnostic criteria for basal insulin (P = 0.03), OST (P = 0.01), and CGIT (P < 0.01). Kappa coefficients, measuring agreement between basal insulin, OST, and CGIT, showed none to moderate agreement at the baseline time point. Conclusion Dexamethasone administration at 0.08 mg/kg, PO, q24h for 7 d worsened insulin dysregulation in adult light-breed horses based on findings of a basal insulin, OST, CGIT, and insulin sensitivity proxy measurements. There was none to moderate agreement between the basal insulin, OST, CGIT for the diagnosis of insulin dysregulation. Clinical relevance Horses administered dexamethasone at a dose of 0.08 mg/kg, PO, q24h for 7 d should be considered insulin dysregulation and appropriate preventative strategies should be implemented. The variability of diagnostic performance of common tests for insulin dysregulation (basal insulin, OST, CGIT) may affect clinical decisions; therefore, performing multiple tests, including proxy measurements, may improve diagnostic accuracy of insulin dysregulation.

Automated summary

The research assessed the effects of dexamethasone on insulin and glucose dynamics in light-breed horses, and evaluated the agreement of different diagnostic tests for insulin dysregulation. Dexamethasone treatment worsened insulin dysregulation, and the variability of common diagnostic tests for insulin dysregulation may impact clinical decisions.