Repeatability of 2 methods for assessment of insulin sensitivity and glucose dynamics in horses.
Authors: Pratt Shannon E, Geor Ray J, McCutcheon L Jill
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary The euglycemic-hyperinsulinemic clamp (EHC) and minimal model analysis of the frequently sampled intravenous glucose tolerance test (FSIGT) are both used to assess insulin sensitivity in horses, yet their reliability had never been formally evaluated. Pratt and colleagues tested six healthy horses using both methods on two occasions over four weeks to determine which provided more consistent, reproducible measurements of insulin sensitivity and glucose dynamics. The EHC demonstrated superior repeatability, with insulin sensitivity measurements showing only 14.1% average day-to-day variation and a strong intraclass correlation coefficient of 0.74, whereas the FSIGT minimal model produced 23.7% variation and a weak ICC of 0.33 for insulin sensitivity. Within the FSIGT, acute insulin response proved highly reproducible (ICC 0.98, 11.7% variation), whilst glucose effectiveness was unreliable (ICC 0.10, 26.4% variation). For equine practitioners and researchers assessing insulin resistance—increasingly relevant given the prevalence of equine metabolic syndrome—the EHC offers greater confidence in serial measurements and longitudinal monitoring, though the FSIGT remains useful for capturing acute insulin secretion dynamics if multiple measurements are averaged to account for inherent variability.
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Practical Takeaways
- •When assessing insulin sensitivity in horses for metabolic or endocrine evaluation, the EHC method provides more consistent and reproducible results than FSIGT minimal model analysis
- •If using FSIGT for glucose dynamics testing, acute insulin response measurements are reliable, but insulin sensitivity estimates should be interpreted with caution given their poor repeatability
- •Sequential testing for metabolic monitoring should preferably use the same method (EHC) to enable meaningful comparison of results, as different methods have substantially different variation profiles
Key Findings
- •Euglycemic-hyperinsulinemic clamp (EHC) demonstrated lower interday variation (CV 14.1%) compared to minimal model FSIGT analysis (CV 23.7%) for insulin sensitivity measurement
- •EHC insulin sensitivity (M/I ratio) showed good repeatability with ICC of 0.74 versus poor repeatability for minimal model Si with ICC of 0.33
- •Minimal model acute insulin response (AIRg) was highly repeatable (ICC 0.98, CV 11.7%) while glucose effectiveness (Sg) had poor repeatability (ICC 0.10, CV 26.4%)
- •EHC is the more reliable method for assessing insulin sensitivity in horses due to superior reproducibility over the 4-week test period