Diagnosis of equine pituitary pars intermedia dysfunction

Equine pituitary pars intermedia dysfunction (PPID) is common in aged horses. The majority of horses respond well to treatment, but treatment is lifelong, meaning accurate diagnosis of PPID is important. Similar to any condition, there is no perfect laboratory test to diagnose PPID and accuracy is affected by the characteristics of the population in which the test is being evaluated. This review details the importance of consideration of clinical factors and diagnostic test accuracy. Basal adrenocorticotrophic hormone (ACTH) concentration is used most frequently in practice and has very good diagnostic accuracy when used in combination with clinical judgement and the correct application of diagnostic thresholds. The thyrotropin-releasing hormone stimulation test can be used in horses with equivocal test results following basal ACTH testing, or to evaluate subtle cases due to its improved accuracy. •Laboratory diagnosis of pituitary pars intermedia dysfunction is not perfect•The characteristics of the population affect laboratory test accuracy•Basal adrenocorticotrophic hormone (ACTH) concentration is most commonly used•ACTH test accuracy is best when interpreted alongside clinical presentation•Thyrotropin-releasing hormone stimulation can be used when basal ACTH is equivocal