Comparison of fasted basal insulin with the combined glucose-insulin test in horses and ponies with suspected insulin dysregulation.

The research investigated and compared two diagnostic methods (Fast Insulin and Combined Glucose-Insulin Test) in the detection of insulin dysregulation (ID) in horses. The study discussed the limitations in using the Fast Insulin method and suggested refining the cutoff values for a more accurate diagnosis.

Research Aim

• The main focus of the study was to compare the effectiveness of Fasting Insulin (FI) and the Combined Glucose-Insulin Test (CGIT) in diagnosing insulin dysregulation (ID) in horses.
• The researchers hypothesized that FI might have lower sensitivity in detecting ID compared to CGIT when using conventional cut-off values.

Methods Employed

• The study examined records from CGITs carried out on horses that had been fasted for about 8 hours.
• The researchers measured serum insulin and glucose concentrations before and for 150 minutes after administering an intravenous bolus of glucose followed by insulin.
• Statistical methods, such as Youden’s index analysis, logistic regression, and Mann-Whitney U tests, were employed to assess the correlation between FI and CGIT values and to evaluate the factors influencing the results.

Results and Observations

• The test results (CGITs) from 62 horses, in total 130 tests, were evaluated.
• Comparison of FI and CGIT showed that FI had a sensitivity of 14.6% and specificity of 100% at a 20μIU/mL cutoff, and a sensitivity of 63.4% and specificity of 87.2% at a cutoff of 5.2μIU/mL.
• There was significant correlation between FI and CGIT results at various measurement intervals and cutoffs. For instance, FI was highly correlated with insulin at 45min (r=0.66) and 75min (r=0.72).
• It was observed that obesity significantly increased the odds of a positive CGIT and older horses were significantly more likely to have a positive CGIT.

Conclusion and Recommendations

• The study concluded that FI showed promising correlation with CGIT results and had satisfactory sensitivity and specificity at lower cutoffs.
• The researchers pointed out the poor sensitivity of FI at conventional cutoff values and suggested that further research should be conducted to establish cutoff values relevant to the fasting period for improved diagnostic precision.