E03 - Evaluation of Commonly used Field-Testing Protocols to Diagnose Insulin Dysregulation and the Association with Laminitis

Background – Insulin dysregulation (ID) consists of hyperinsulinemia (HI) with or without insulin resistance (IR). Various protocols have been proposed but not evaluated to determine laminitis risk.

Hypothesis/Objectives – Evaluate the oral sugar test (OST) and 2-step insulin tolerance test to diagnose ID the association with laminitis.

Animals – One hundred and forty-four ponies.

Methods – Insulin concentrations > 20 or > 50 µIU/mL at baseline or > 45 or > 65 µIU/mL at 60 or 90 minutes after oral administration of 0.45 mL/kg of corn syrup defined HI. Reduction of blood glucose concentration to < 50% of baseline after intravenous administration of 0.1 IU/kg insulin was defined IR. Laminitis was defined as modified-Obel score > 1. Descriptive statistics and receiver operating characteristic curves were performed.

Results – Overall, 31% ponies had laminitis. Basal HI was present in 15% (20-µIU/mL cut-off) and 10% (50-µIU/mL cut-off) of ponies. On OST, HI was present in 42% and 45% (45-µIU/mL cut-off at 60 and 90 minutes respectively), and 35% and 38% (60-µIU/mL cut-off at 60 and 90 minutes respectively) of ponies. Fifty-three percent were IR. All ponies with basal HI had post-OST HI; however, 69% with post-OST HI did not have basal HI. Of IR ponies, 77% did not have basal HI and 27% did not have post-OST HI. A 45-µIU/mL cut-off at 60 minutes and IR had better sensitivities and specificities, with laminitis as the outcome.

Conclusions and clinical importance – With an incomplete overlap between HI and IR, performing both tests improves evaluation of ID and laminitis.