Up to 64% of ponies without clinical signs of PPID have plasma ACTH concentrations that are above the upper “normal” reference interval (Knowles et al., 2018). Of these ponies, 70% had ACTH values fall to within normal without treatment by the following spring. Possible theories for the difference between the tested ponies and horse reference ranges include: (1) ponies may have a greater seasonal ACTH response than horses, (2) there may be cross reactivity with other peptides released at the same time, or (3) ponies were in an early stage of PPID. The take-home message: Caution should be used when interpreting ACTH concentrations in ponies during.
Possible theories for the difference between the tested ponies and horse reference ranges include: (1) ponies may have a greater seasonal ACTH response than horses, (2) there may be cross reactivity with other peptides released at the same time, or (3) ponies were in an early stage of PPID.
Reference: EJ Knowles, MC Moreton-Clack, S Shaw, PA Harris, J Elliott, NJ Menzies-Gow. Plasma adrenocorticotropic hormone (ACTH) concentrations in ponies measured by two different assays suggests seasonal cross reactivity or interference. Equine Veterinary Journal 50:5:672-7, 2018