Comparison of fasted basal insulin with the combined glucose-insulin test in horses and ponies with suspected insulin dysregulation.
Authors: Olley R B, Carslake H B, Ireland J L, McGowan C M
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Fasting Insulin versus Combined Glucose-Insulin Testing for Equine Insulin Dysregulation Insulin dysregulation (ID) is increasingly recognised in equine practice, but diagnostic protocols remain inconsistent; whilst fasting insulin (FI) measurement is recommended for standardisation, few studies have directly validated it against dynamic testing. Olley and colleagues compared FI measurements with the combined glucose-insulin test (CGIT)—a 150-minute dynamic assessment following intravenous glucose and insulin administration—in 130 CGIT evaluations from 62 horses with suspected ID. Using conventional cut-offs (20 µIU/mL), FI demonstrated poor sensitivity (14.6%) despite perfect specificity, but lowering the threshold to 5.2 µIU/mL improved sensitivity to 63.4% whilst maintaining reasonable specificity at 87.2%; importantly, FI correlated significantly with mid-test and late insulin responses (r=0.66–0.72) and overall insulin load. The findings suggest that whilst FI cannot replace CGIT as a definitive diagnostic tool, it may serve as a practical screening measure if cut-off values are adjusted downward from currently recommended thresholds, though practitioners should recognise that older and obese horses are at substantially higher risk of positive results. Further research establishing context-specific cut-offs for the 8-hour fasting protocol is needed before FI can be reliably adopted as a standalone diagnostic in routine practice.
Read the full abstract on PubMed
Practical Takeaways
- •Fasting insulin testing alone at standard cut-offs (20μIU/mL) will miss many horses with insulin dysregulation; consider dynamic testing (CGIT) for suspect cases or use lower cut-offs (5.2μIU/mL) if relying on fasting values
- •Obesity and advancing age are risk factors for insulin dysregulation; prioritize weight management and metabolic screening in older, overweight horses
- •Fasting insulin correlates well with dynamic test results, making it a practical screening tool when standardized to appropriate fasting periods and cut-off values
Key Findings
- •Fasting insulin had poor sensitivity (14.6%) for detecting insulin dysregulation at conventional cut-off of 20μIU/mL but improved sensitivity (63.4%) at lower cut-off of 5.2μIU/mL
- •Fasting insulin correlated significantly with combined glucose-insulin test parameters including insulin at 45min (rs=0.66) and 75min (rs=0.72)
- •Obesity was significantly associated with increased odds of positive CGIT, and horses with positive CGIT were significantly older
- •Current fasting insulin cut-off values may not be appropriate for the 8-hour fasting protocol used in this study