Summary Insulin dysregulation is the hallmark of equine metabolic syndrome and has received attention because of its direct association with laminitis. In the absence of an adequate treatment for laminitis, a focus on prophylaxis is needed, making early detection of individuals at risk of developing laminitis one of the main challenges in equine endocrinology. Recent studies have shown that insulin dysregulation goes beyond tissue insulin resistance and it is now demonstrated that the equine enteroinsular axis plays a major role in insulin secretion and equine hyperinsulinaemia. In this review, we discuss the different tests currently available to diagnose insulin dysregulation in horses: the ones investigating tissue insulin resistance and those investigating the enteroinsular axis, detailing their goals, practicalities and limitations. This review supports the contention that the diagnosis of equine insulin dysregulation should now be based on the investigation of both tissue insulin resistance and the equine enteroinsular axis. Regardless of the tests used many factors of variation, such as breed, diet, fasting state or season, have been identified and could potentially confound the results of a specific test. Therefore, careful interpretation of the results of a given test in each individual situation is required to optimise the detection of horses at risk of laminitis.