Diagnostic Testing for Equine Endocrine Diseases: Confirmation Versus Confusion.
Authors: D. McFarlane
Journal: The Veterinary clinics of North America. Equine practice
Summary
# Editorial Summary McFarlane's 2019 review addresses a critical gap in equine practice: whilst PPID and EMS represent the two primary endocrine conditions affecting horses, diagnostic confusion remains widespread and often leads to unnecessary lifelong pharmacotherapy. The author conducted a comprehensive examination of current diagnostic protocols, emphasising how laboratory interpretation must be contextualised against multiple horse-specific variables—including breed genetics, age, seasonal variation, coat characteristics, nutritional status, concurrent illness, and geographical location—rather than applied as absolute cut-off values. Elevated plasma ACTH remains diagnostic for PPID, yet baseline and TRH-stimulated measurements are influenced substantially by these confounding factors; similarly, insulin dysregulation in EMS requires differentiation between primary insulin resistance and excessive postprandial insulin secretion, each demanding distinct testing approaches for accurate diagnosis. The practical implication is significant: clinicians must integrate laboratory results with comprehensive phenotypic assessment and patient history to avoid over-diagnosing endocrine disease and subjecting otherwise healthy animals to indefinite medication—a particularly important consideration given the potential side-effects and cost implications of long-term treatment. This framework emphasises that diagnostic confidence demands methodological rigour and nuanced interpretation rather than reliance on single-point reference ranges.
Read the full abstract on PubMed
Practical Takeaways
- •Do not diagnose PPID based on elevated ACTH alone—always consider the horse's age, breed, season, body condition, and health status before starting lifelong medication
- •Recognize that EMS diagnosis requires identifying which type of insulin dysregulation is present (resistance vs. postprandial excess) as this determines appropriate management strategy
- •When interpreting endocrine test results, use clinical judgment and contextual horse factors rather than treating numbers in isolation to avoid unnecessary long-term drug therapy
Key Findings
- •Only 2 common endocrine diseases exist in horses (PPID and EMS), yet diagnosis remains clinically confusing and frequently misapplied
- •ACTH concentration is affected by multiple non-pathological factors including breed, age, body condition, illness, coat color, geography, diet, and season, leading to overdiagnosis and unnecessary lifelong treatment
- •Insulin dysregulation in EMS can result from either insulin resistance or excessive postprandial insulin release, each requiring different diagnostic tests for accurate differentiation
- •Relying on laboratory results alone without considering individual horse factors commonly results in inappropriate diagnosis and unnecessary pharmacological treatment