Evaluating insulindysregulation in horses: A two-step insulin-tolerance test using porcine zinc insulin.
Authors: Grob A J, Delarocque J, Feige K, Warnken T
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Insulin-Tolerance Testing with Porcine Zinc Insulin Diagnosing insulin dysregulation in horses requires reliable insulin-tolerance tests (ITT), yet the gold-standard agent—recombinant human insulin (RHI)—remains inaccessible to many practitioners, prompting researchers to evaluate whether the more readily available veterinary formulation porcine zinc insulin (PZI) could serve as an effective alternative. Grob and colleagues conducted a randomised crossover study on twelve Icelandic horses, administering both RHI and PZI at identical doses (0.1 IU/kg) and comparing the resulting glucose and insulin dynamics, with particular attention to classification consistency across the two protocols. Whilst blood glucose concentrations and absolute percentage reductions showed no significant difference between tests (P = 0.053), the choice of insulin substantially altered clinical interpretation: RHI classified four horses as insulin-resistant, whereas PZI classified seven as such using the traditional 50% glucose reduction cut-off at 30 minutes. The researchers identified an adjusted threshold of 40% glucose reduction for PZI-based testing that improved diagnostic accuracy according to the Youden index, establishing a practical pathway for practitioners to adopt this veterinary-approved formulation. For equine professionals seeking to screen for insulin dysregulation, PZI represents a pragmatic substitute to RHI provided the revised cut-off value is applied, though this adjustment underscores the importance of using protocol-specific reference ranges rather than interchanging insulin formulations without corresponding diagnostic thresholds.
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Practical Takeaways
- •PZI can be used as a practical substitute for RHI in insulin-tolerance testing since it is veterinary-approved and more accessible to practitioners
- •When using PZI for insulin-tolerance testing, apply a 40% glucose reduction threshold at 30 minutes rather than the standard 50% to improve diagnostic accuracy for insulin resistance
- •No safety concerns were observed with either insulin formulation, making PZI a viable alternative for practitioners without access to RHI
Key Findings
- •Porcine zinc insulin (PZI) and recombinant regular human insulin (RHI) showed good correlation (r = 0.88; P < 0.001) in insulin-tolerance testing
- •Blood glucose concentrations and percentage reduction did not differ significantly between ITT-RHI and ITT-PZI (P = 0.053)
- •Classification of insulin resistance differed between insulins: 4/12 horses classified as IR with RHI versus 7/12 with PZI using 50% glucose reduction threshold
- •An adjusted cut-off value of 40% blood glucose reduction at 30 minutes for ITT-PZI resulted in better test performance based on Youden index