Equine Endocrine Disease: Challenges With Case Definition for Research

•Equine endocrine research requires case definition for inclusion.•Defining a case for research may be different from criteria for clinical diagnosis.•Scientists should be aware of research into and validation of the use of biomarkers.•Reference intervals and clinical decision limits are not the same. Equine endocrine disease is an important area for equine research, requiring an appropriate case definition for inclusion and criteria for exclusion from disease. Defining a case for research may be different from criteria for clinical diagnosis. Further, clinical diagnosis recommendations have been changing regularly, making this area challenging for equine scientists. This review discusses the diagnosis of major equine endocrine diseases, pituitary pars intermedia dysfunction, equine metabolic syndrome and insulin dysregulation, focusing on the most appropriate diagnostic methods for research case definitions. Different diagnostic methods, including use of reference intervals and clinical decision limits, will be discussed with their relative merits for use in case definition for research.