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Reference intervals: an essential, expanding, and occasionally equivocal standard.

This issue of Veterinary Clinical Pathology includes 2 articles on reference intervals (RI). The authors of these articles draw the salient conclusion that RI require updating because of changes in reference populations and analytical methodology. George et al stress that use of older RI could lead to misinterpretation of clinical data. This is true whenever an RI does not accurately reflect the population for which it is used, and therein lies the dilemma that faces all veterinarians who use RI to make clinical decisions regarding health or the absence thereof: ‘‘Do the RI you use accurately reflect your patient population and current laboratory methods?’’ Accordingly, it is recommended that each laboratory develop RI specific to its methods and patient population. However, developing RI is a costly and time-consuming endeavor, especially for laboratories that provide diagnostic testing for a multitude of species. Add to this the potential differences in RI for various subgroups based on age, breed, gender, and husbandry, and laboratory-specific RI become an overwhelming prospect. The need for separate RI based on physiology and geography is a focus of many articles published in Veterinary Clinical Pathology. In wildlife species, RI are required for monitoring the health of endangered species and the ecosystems in which they live. The breadth of articles published in Veterinary Clinical Pathology, in both captive and free-ranging populations, reflects this growing need. Despite this expanding body of knowledge, the question often remains, ‘‘Can published RI be used in a broader context in diverse clinical situations?’’ The primary problem with using published RI is the frequent lack of detail regarding size and demographics of the reference population, the quality and method of analysis, and the statistical procedures by which RI were determined. Müller et al discuss the difficulty in making a clinical diagnosis using published RI when this crucial information is not provided. The Clinical and Laboratory Standards Institute (CLSI) and International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) recently published updated guidelines for the determination of reference intervals, which were summarized by Geffré at al in a recent issue of Veterinary Clinical Pathology. The basic procedures for determining RI have not changed appreciably over the years. However, in response to concerns over the expense of establishing de novo RI, the updated guidelines include statistical methods for determining RI from smaller sample sizes and specific recommendations for validation of RI transferred from other sources. Examples of these 2 procedures were recently published in this journal. Although the quality of published RI studies has improved, there still is a need for greater consistency in RI determination in the veterinary community. Contributing to this effort, the Quality Assurance and Standards Committee of the American Society for Veterinary Clinical Pathology (ASVCP) is formulating veterinary-specific guidelines for determining RI based on the 2008 CLSI guidelines. With transference and validation now accepted as a viable alternative to establishing de novo RI, emphasis will be on quality of analysis, which is defined by the total error (TE) of a method. Establishing goals for total allowable error (TEA) for analytes measured in animal samples will facilitate the assessment of analytical quality and the ability to use transference. Veterinary clinicians, pathologists, and researchers must work together to expand the body of knowledge concerning RI in a variety of species, under a variety of conditions, and by a variety of methods. Developing useful and practical RI only will be achieved if there is consistency in RI determination, full documentation of study details and method quality, and ongoing publication of results. The ASVCP appreciates the contribution of all our colleagues to this growing and challenging enterprise.