Recommendations from the Australian and New Zealand Equine Endocrine Group and the interpretation of plasma endogenous ACTH concentrations for the diagnosis of pituitary pars intermedia dysfunction (PPID).

The article examines the validity of recent recommendations from the Australian and New Zealand Equine Endocrine Group concerning the interpretation of plasma ACTH concentrations for diagnosing pituitary pars intermedia dysfunction (PPID) in horses.

Understanding the Context

• The research scrutinizes the interpretation of Adrenocorticotropic Hormone (ACTH) levels, crucial for diagnosing Pituitary Pars Intermedia Dysfunction (PPID) in horses. This condition affects the pituitary gland, leading to a series of health problems in horses.
• The researchers argue that the new guidelines for ACTH measurement set by the Australian and New Zealand Equine Endocrine Group lack supporting evidence from previous studies and appear to arbitrarily enlarge the cut-off values for PPID diagnosis.

Identification of Key Issues

• The researchers list three key issues: firstly, the “grey zones” or indeterminate areas start from a high-end variation of what’s considered normal. Secondly, these grey zones seem to be extrapolated from healthy horses instead of horses with PPID. Thirdly, previous research data that included both healthy and PPID-affected horses were not properly factored into the new guidelines.

Interpretation of Previous Research

• In their analysis, the researchers refer to key studies conducted both in the Northern and Southern Hemispheres. A study in the UK utilized a group of clinically normal horses to determine an upper reference limit for ACTH, which served as a cut-off value. This cut-off influenced the U.S.-based Equine Endocrinology Group to formulate an ‘equivocal zone’ for interpreting ACTH levels.
• Another study based in Perth (Australia) followed a similar methodology to the UK research, deriving an upper reference limit based on ACTH cut-offs. However, this limit changes throughout the year.

Questions Raised

• The researchers question the validity of this approach, questioning the methods used to confirm the normal health status of the horses used in the studies, the appropriateness of using younger controls, and, most importantly, the apparent lack of comparison between healthy and PPID-affected horses in the data used to derive the ACTH interpretation guidelines.