Repeatability of the combined glucose-insulin tolerance test and the effect of a stressor before testing in horses of 2 breeds.
Authors: Bröjer J, Lindåse S, Hedenskog J, Alvarsson K, Nostell K
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Repeatability of the Combined Glucose-Insulin Tolerance Test The combined glucose-insulin tolerance test (CGIT) has become an important diagnostic tool for identifying insulin resistance in horses, particularly given the established link between IR and laminitis. Brojer and colleagues assessed whether this test produces consistent results across repeated measurements and investigated how breed and environmental stress might influence outcomes, using nine Standardbred and nine Icelandic horses tested on two occasions three weeks apart, with a subset undergoing an additional test following transportation stress. Whilst insulin curve parameters demonstrated strong repeatability, glucose dynamics showed poor repeatability between test occasions—a critical finding compounded by significant breed differences and stress-induced variation in glucose response, though not insulin response. These results suggest that relying solely on glucose parameters when diagnosing IR risks both false positives and false negatives, and highlight the need for practitioners to consider breed-specific reference ranges and testing conditions. For clinical decision-making, insulin curve measurements should be weighted more heavily than glucose dynamics in the CGIT, and multiple testing occasions may be warranted when making IR diagnoses with significant management or therapeutic implications.
Read the full abstract on PubMed
Practical Takeaways
- •Do not rely solely on glucose curve results from a single CGIT to diagnose insulin resistance, as these results are unreliable and variable
- •Insulin curve parameters are more trustworthy for repeated assessments and longitudinal monitoring of IR status
- •Be aware that breed and recent stress (e.g., transport) can significantly influence glucose responses during testing, potentially leading to misinterpretation of results
Key Findings
- •Glucose curve parameters of the CGIT showed low repeatability between test occasions 3 weeks apart
- •Insulin curve parameters of the CGIT demonstrated high repeatability across repeated testing
- •Breed differences existed in glucose dynamics, with Standardbreds and Icelandic horses responding differently to the CGIT
- •Transportation stress affected glucose dynamics but not insulin dynamics on the CGIT