EMS can be diagnosed by your veterinarian based on history, physical examination findings, radiographic evaluation of the feet, and laboratory tests.  Physical examination involves an evaluation of body condition and looking for evidence of regional adiposity.

Screening tests for insulin resistance include measurements of insulin and glucose.  Horses should be removed from pasture and fed only grass hay/water for 12 hours prior to blood sample collection.  Also, cortisol and epinephrine released from stress or pain can elevate insulin levels.  Therefore, sampling conditions are important when testing for insulin resistance, and testing should be delayed in a horse currently suffering from laminitis until stress and pain has subsided.  Insulin > 20 µU/mL provides evidence of IR.  If elevated insulin is not detected, but other components of EMS are present, a dynamic test of insulin sensitivity can be performed (glucose tolerance test or a combined glucose-insulin tolerance test).

Given the similarities between EMS and Cushing’s, horses with regional adiposity and laminitis should also be tested for Cushing’s in addition to EMS, especially horses over 15 years of age who experience delayed shedding or increases in drinking and urination. Diagnostic tests for Cushing’s include ACTH (adrenocorticotropin hormone) and dexamethasone suppression tests.  In horses and ponies with Cushings, ACTH (adrenocorticotropin hormone) is elevated and cortisol is not suppressed by dexamethasone administration (dexamethasone suppression test).  These tests should be performed outside the late summer/fall period(Aug-Nov), which are times of the year when false positives occur in healthy horses and ponies.

*This project was supported by Agriculture and Food Research Initiative competitive grant no. 2009-55205-05254 from the USDA National Institute of Food and Agriculture Animal Genome Program.