Basal insulin concentrations can be used as a screening test for Equine Metabolic Syndrome (EMS) and can also have prognostic value when evaluating cases of pituitary pars intermedia dysfunction (PPID, equine Cushing’s syndrome). Note however only approximately 30% of horses with EMS have fasting hyperinsulinaemia and dynamic testing with an in-feed oral glucose challenge test is typically recommended to capture most cases of insulin resistance.
Feeding can cause significant increases in serum insulin concentrations. Therefore it is preferable to measure basal insulin concentrations after fasting (6 hours minimum).
In-feed oral glucose challenge test
The in-feed oral glucose challenge test offers a more sensitive means of identifying horses with insulin resistance, one of the hallmarks of EMS. Generally, only the post-prandial insulin concentration is interpreted. Therefore there is no need to collect a basal serum sample for insulin measurement prior to the oral glucose challenge. Measurement of triglycerides and fasting glucose concentrations may be additional tests alongside characteristic changes in the clinical picture that can be helpful in formulating a diagnosis of EMS. Note however very few horses with EMS exhibit fasting hyperglycaemia.
Basal insulin: Collect a serum sample after a minimum of 6 hours fast.
In-feed oral glucose challenge test:
- Fast the horse/pony overnight (12 hours).
- Give a non-glycaemic feed (eg. chaff) containing 1g/kg bodyweight glucose or dextrose powder mixed with a little water to aid mixing/ingestion.
- Collect a serum sample two hours after ingestion of the feed for measurement of insulin concentrations.
- Separate the serum sample from the red cells before sending to the laboratory.
Special handling/shipping requirements:
Serum insulin is unstable at room temperature and must be kept chilled. Send the separated serum samples with gel ice packs to the laboratory as soon as possible. If testing cannot be performed within 24 hours, freeze the separated serum.