Deciphering reference intervals and clinical decision limits in equine endocrine diagnostic testing.
Authors: Ireland Joanne, McGowan Catherine
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary When interpreting endocrine test results in equine practice, clinicians often conflate reference intervals (RIs) with clinical decision limits (CDLs), yet these serve fundamentally different purposes: RIs indicate whether an individual horse falls within the healthy range, whilst CDLs identify those with actual disease or elevated risk of adverse outcomes. Ireland and McGowan's 2023 review clarifies this distinction and introduces the concept of 'grey zones'—ranges of test values where diagnostic accuracy is insufficient to support confident clinical decision-making, thereby avoiding the false certainty of binary cut-off interpretations. Rather than forcing results into simply 'positive' or 'negative' categories, incorporating these intermediate zones acknowledges the biological reality that test performance varies across different result ranges and allows for more nuanced clinical reasoning. The authors explore how both RIs and CDLs should be applied within equine endocrinology specifically, providing evidence-based guidance for practitioners interpreting thyroid function, adrenocortical status, and metabolic parameters in their diagnostic work. Understanding these distinctions will refine how farriers, vets, physiotherapists and nutritionists use laboratory data to inform management decisions and communicate findings to horse owners.
Read the full abstract on PubMed
Practical Takeaways
- •Don't treat a single cut-off value as definitive—use both reference intervals and clinical decision limits appropriately to distinguish healthy horses from those with endocrine disease
- •Recognize that some test results fall in a 'grey zone' where the test cannot clearly distinguish disease state; these uncertain results require clinical correlation and possible retesting rather than immediate diagnostic or treatment decisions
- •Understand that RIs tell you if a horse is 'normal' compared to a healthy population, while CDLs tell you if a horse has or is at risk for a specific disease—these serve fundamentally different diagnostic purposes
Key Findings
- •Reference intervals (RIs) estimate whether an individual is healthy, while clinical decision limits (CDLs) identify individuals with specific disease states or increased risk of adverse outcomes
- •A 'grey zone' of uncertain test results between positive and negative thresholds improves diagnostic decision-making by avoiding binary classification constraints
- •Distinction between RIs and CDLs is frequently confused in clinical practice despite their different purposes in endocrine biomarker interpretation