Diagnosis of equine insulin dysregulation (ID) begins with a resting basal insulin measurement, followed by dynamic oral challenge testing when basal results are equivocal or when greater sensitivity is required. ID is defined as any combination of basal hyperinsulinemia, postprandial hyperinsulinemia on dynamic testing, or peripheral tissue insulin resistance, and is the central component of equine metabolic syndrome (EMS).Journal of Vete…+1
Diagnosis
Basal insulin is the first-line screening test. Blood is collected from a horse that has been fasted for 8–10 hours, or at minimum has had hay withheld overnight.Journal of Vete… Serum or heparinized plasma is the preferred sample type; ethylenediaminetetraacetic acid (EDTA) tubes produce significantly lower insulin concentrations and should not be used.Journal of Vete… Samples analyzed within 3 days at 20°C or within 8 days at 4°C are stable; serum and heparinized samples perform equivalently within those windows.Journal of Vete… Basal insulin alone has lower sensitivity than dynamic testing for detecting ID, and a normal resting result does not exclude the diagnosis.Journal of Vete…
Dynamic oral challenge testing is the preferred method for diagnosing ID and is more sensitive than basal testing alone. The oral sugar test (OST) and oral glucose test (OGT) are the most commonly used dynamic tests; both evaluate the insulin response to an oral carbohydrate stimulus and are considered equivalent for identifying horses with ID.Journal of Vete…+1 The OST uses commercial corn syrup at doses of 0.15–0.45 mL/kg body weight administered to a fasted horse, with blood collected for insulin measurement at 60–90 minutes post-administration.Journal of Vete…+1 Higher doses have been proposed to improve diagnostic accuracy, though this remains controversial, and higher volumes may be impractical in larger horses.Journal of Vete… The OGT follows a similar principle using oral dextrose.The Veterinary… Both tests require an 8–10 hour fast and approximately 2 hours to complete.Journal of Vete…
The 2-step insulin sensitivity test evaluates peripheral tissue insulin resistance and can be performed within 30 minutes without fasting, making it practical for field use.Journal of Vete…+1 It measures the glucose response to an intravenous insulin challenge.Journal of Vete… The combined thyrotropin-releasing hormone (TRH) stimulation test and 2-step insulin sensitivity test can be performed simultaneously to diagnose pituitary pars intermedia dysfunction (PPID) and ID concurrently in a single visit, with combined testing producing equivalent results to independent testing.Journal of Vete…
Agreement between basal insulin, OST, and combined glucose-insulin test (CGIT) is none to moderate, meaning a horse may test positive on one modality and negative on another.Canadian Veteri… Performing multiple tests, including insulin sensitivity proxy measurements, improves diagnostic accuracy.Canadian Veteri… Dynamic oral challenge testing is considered superior to basal measures alone for reliable identification of ID.Journal of Vete…
Dexamethasone administration worsens ID — horses receiving dexamethasone at 0.08 mg/kg PO q24h for 7 days show increased insulin and glucose responses on basal insulin, OST, and CGIT testing.Canadian Veteri… Any horse on this corticosteroid regimen should be considered at risk for ID and managed accordingly.Canadian Veteri…
Assay selection materially affects insulin values. No equine-specific insulin antibody assay is commercially available, and different immunoassay platforms produce discrepant results.BMC Veterinary… Results should always be interpreted in the context of the specific assay used by the reference laboratory, and cross-laboratory comparisons require caution.BMC Veterinary…
Management
The primary management goal is reducing blood insulin concentrations to minimize laminitis risk.Journal of Vete… The risk of laminitis increases with higher blood insulin concentrations, making normalization of insulin the central therapeutic target.Journal of Vete…
First-line management is dietary and exercise-based. Recommended interventions include decreasing sugars and starches in the diet, increasing exercise, monitoring and maintaining hoof health, and restricting energy intake in obese animals.Journal of Vete… In many cases, blood insulin concentrations normalize with diet and exercise alone, but this response can be delayed or incomplete.Journal of Vete…
When diet and exercise produce a suboptimal response, pharmacological treatment is warranted. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have been investigated as pharmacological treatment for ID in horses, based on their established use in managing type 2 diabetes mellitus in humans.Journal of Vete… Velagliflozin, an SGLT2i, lowers blood glucose concentrations by inhibiting glucose reuptake in the proximal renal tubule, causing glucosuria.Journal of Vete…
EMS management is a long-term commitment requiring sustained dietary discipline by the owner and ongoing veterinary guidance.Journal of Vete… Obesity and regional adiposity are modifiable risk factors that should be targeted alongside insulin-specific interventions.Journal of Vete…+1
| Test | Protocol | Key Strength | Key Limitation |
|---|---|---|---|
| Basal insulin | Single fasted sample; serum or heparinized plasma | Simple, no fasting challenge required | Lower sensitivity than dynamic testing; normal result does not exclude ID Journal of Vete… |
| Oral sugar test (OST) | 0.15–0.45 mL/kg corn syrup PO; 8–10 h fast; insulin at 60–90 min | Field-practical; equivalent to OGT for ID detection | Corn syrup not globally available; sugar composition varies by batch Journal of Vete…+1 |
| Oral glucose test (OGT) | Oral dextrose; 8–10 h fast; insulin response measured | Equivalent to OST for ID detection | Requires 8–10 h fast and ~2 h to complete Journal of Vete…+1 |
| 2-step insulin sensitivity test | IV insulin challenge; no fasting required; completes in 30 min | No fast needed; field-practical; assesses tissue IR | Does not evaluate enteroinsular axis Journal of Vete…+1 |
| Combined TRH + 2-step IST | Simultaneous TRH and insulin injection; single visit | Diagnoses PPID and ID concurrently | Minor risk of false positives/negatives on combined testing Journal of Vete… |
Would you like guidance on specific dietary targets — such as non-structural carbohydrate thresholds — for managing the EMS horse?