Comparison among the euglycemic-hyperinsulinemic clamp, insulin-modified frequently sampled intravenous glucose tolerance test, and oral glucose tolerance test for assessment of insulin sensitivity in healthy Standardbreds.

OBJECTIVE: To compare, in horses, estimates of insulin sensitivity obtained from minimal model analysis (MMA) of a frequently sampled IV glucose tolerance test (FSIGTT) with estimates from the euglycemic-hyperinsulinemic clamp (EHC) and to evaluate the validity of surrogate estimates of insulin sensitivity derived from an oral glucose tolerance test (OGTT). ANIMALS: 18 mature Standardbreds (mean ± SD body weight, 428.9 ± 35.9 kg; mean ± SD body condition score, 4.4 ± 1.0 [on a scale of 1 to 9]). PROCEDURES: All horses underwent at least 2 of the 3 procedures (EHC [n = 15], insulin-modified FSIGTT [18], and OGTT [18]) within a 10-day time frame to evaluate insulin sensitivity.
RESULTS: Insulin sensitivity variables derived from the EHC and FSIGTT were strongly correlated (r = 0.88). When standardized to the same units of measure, these measures were still strongly correlated (r = 0.86) but were not equivalent. Area under the curve, peak insulin concentration, insulin concentration at 120 minutes, and 2 calculated indices from glucose and insulin data from the OGTT were significantly correlated with the EHC- and FSIGTT-derived estimates of insulin sensitivity. CONCLUSIONS AND CLINICAL RELEVANCE: In healthy Standardbreds with moderate body condition score, insulin sensitivities from the EHC and FSIGTT were strongly correlated but not equivalent. Estimates derived from an OGTT also may be useful to estimate insulin sensitivity.